Professor Smith- I am not sure about this chapter. I am having some difficulties here and there. When I figure out exactly what the issues are, I will email you.
......!!!!!!!!...................................
12:11:30 query 3.1.66 (was 3.5.6). f+g, f-g, f*g and f / g for | x | and x.
What are f+g, f-g, f*g and f / g and what is the domain and range of each?......!!!!!!!!...................................
RESPONSE --> f+g=|x|+x= domain and range are all real numbers f-g= |x|-x= domain and range are all real numbers f*g= |x|*x= -x^2 or x^2 x not equal to 0 f/g= |x|/x= x or -x x not equal to 0
.................................................
......!!!!!!!!...................................
12:12:10 ** The domain of f is all real numbers and its range is all positive numbers. The domain of g is all real numbers and its range is all real numbers.
We recall that if x < 0 it follows that | x | = -x, whereas for x > 0 we have | x | = x. The domain of f + g is all real numbers. f + g = | x | + x. Since for negative x we have | x | = -x, when x < 0 the value of f + g is zero. For x = 0 we have f + g = 0 and for x > 0 we have f + g > 0, and f + g can take any positive value. More specifically for positive x we have f + g = 2x, and for positive x 2x can take on any positive value. The range of f + g is therefore all non-negative real numbers. The domain of f - g is all real numbers. f - g = | x | - x. Since for positive x we have | x | = x, when x > 0 the value of f - g is zero. For x = 0 we have f + g = 0 and for x < 0 we have f - g > 0, and f + g can take any positive value. More specifically for negative x we have f - g = -2x, and for negative x the expression -2x can take on any positive value. The range of f - g is therefore all non-negative numbers. The domain of f * g is all real numbers. f * g = | x | * x. For x < 0 then f * g = -x * x = -x^2, which can take on any negative value. For x = 0 we have f * g = 0 and for x > 0 we have f * g = x^2, which can take on any positive value. The range of f * g is therefore all real numbers. The domain of f / g = | x | / x is all real numbers for which the denominator g is not zero. Since g = 0 when x = 0 and only for x = 0, the domain consists of all real numbers except 0. For x < 0 we have | x | / x = -x / x = -1 and for x > 0 we have | x | / x = x / x = 1. So the range of f / g consists of just the value 1 and -1; we express this as the set {-1, 1}. **......!!!!!!!!...................................
RESPONSE --> okay
.................................................
......!!!!!!!!...................................
12:14:21 query 3.1.70 (was 3.5.10). f+g, f-g, f*g and f / g for sqrt(x+1) and 2/x.
What are f+g, f-g, f*g and f / g and what is the domain and range of each?......!!!!!!!!...................................
RESPONSE --> f+g= sqrt x+1+2/x f-g= (sqrtx+1)-2/x f*g= (sqrtx+1)*2/x f/g= (sqrtx+1)/2/x
.................................................
......!!!!!!!!...................................
12:15:55 ** The square root is always positive and the argument of the square root must be nonnegative, so sqrt(x + 1) is defined only when x+1 > 0 or x > -1. So the domain of f is all real numbers greater than or equal to -1 and its range is all positive numbers.
The function g(x) = 2/x is defined for all values of x except 0, and 2/x = y means that x = 2 / y, which gives a value of x for any y except 0. So the domain of g is all real numbers except 0 and its range is all real numbers except 0. Any function obtained by combining f and g is restricted at least to a domain which works for both functions, so the domain of any combination of these functions excludes values of x which are less than -1 and x = 0. The domain will therefore be at most {-1,0) U (0, infinity). Other considerations might further restrict the domains. The domain of f + g is {-1,0) U (0, infinity). There is no further restriction on the domain. The domain of f - g is {-1,0) U (0, infinity). There is no further restriction on the domain. The domain of f * g is {-1,0) U (0, infinity). There is no further restriction on the domain. The domain of f / g = | x | / x is {-1,0) U (0, infinity) for which the denominator g is not zero. Since the denominator function g(x) = 2/x cannot be zero there is no further restriction on the domain. **......!!!!!!!!...................................
RESPONSE --> I see now that the domain and range was what was being asked for in this problem. I also see how the domain and range work in these equations.
.................................................
......!!!!!!!!...................................
12:21:29 query 5.1.16 (was 3.5.20?). f(g(4)), g(f(2)), f(f(1)), g(g(0)) for |x-2| and 3/(x^2+2)
Give the requested values in order and explain how you got each.......!!!!!!!!...................................
RESPONSE --> f(g(4))=|3/18-2|= 33/18 g(4)=3/18
g(f(2))=3/18 or 3/2= not a function f(2)= 4 or 0 f(f(1))=1 f(1)=1 g(g(0))=3/17/4= 3*4/17= 12/17 g(0)=3/2.................................................
......!!!!!!!!...................................
12:21:44 ** f(g(4)) = | g(4) - 2 | = | 3 / (4^2 + 2) - 2 | = | 3/18 - 2 | = | 1/6 - 12/6 | = | -11/6 | = 11/6. g(f(2)) = 3 / (f(2)^2 + 2) = 3 / ( | 2-2 | ) ^2 + 2) 3 / (0 + 2) = 3/2. f(f(1)) = | f(1) - 2 | = | |1-2| - 2 | = | |-1 | - 2 | = | 1 - 2 | = |-1| = 1. g(g(0)) = 3 / (g(0)^2 + 2) = 3 / ( (3 / ((0^2+2)^2) ^2 + 2)) = 3 / (9/4 + 2) = 3/(17/4) = 12/17. **
......!!!!!!!!...................................
RESPONSE --> ok
.................................................
......!!!!!!!!...................................
12:23:18 query 5.2.16 (was 3.5.30). Domain of f(g(x)) for x^2+4 and sqrt(x-2)
What is the domain of the composite function?......!!!!!!!!...................................
RESPONSE --> I am having trouble with this.
.................................................
......!!!!!!!!...................................
12:24:23 ** The domain of g(x) consists of all real numbers for which x-2 >= 0, i.e., for x >= -2. The domain is expressed as {-2, infinity}.
......!!!!!!!!...................................
RESPONSE --> No wonder- I didn't expect this to be in assignment 26. I see now how to do this and I will work on it until I understand it more.
.................................................
......!!!!!!!!...................................
12:24:36 The domain of f(x) consists of all real numbers, since any real number can be squared and 4 added to the result.
The domain of f(g(x)) is therefore restricted only by the requirement for g(x) and the domain is {-2, infinity}. **......!!!!!!!!...................................
RESPONSE --> ok
.................................................
......!!!!!!!!...................................
12:31:40 query 5.1.26 (was 3.5.40). f(g(x)), g(f(x)), f(f(x)), g(g(x)) for x/(x+3) and 2/x
Give the four composites in the order requested and state the domain for each.......!!!!!!!!...................................
RESPONSE --> f(g(x)=x+2, so x not equal to -2
g(f(x))= sqrtx, x all positive real numbers f(f(x))= not sure how to do this one g(g(x))= (sqrtx-6), x= all positive real numbers.................................................
......!!!!!!!!...................................
12:38:31 ** The domain of f(x) is all x except -3. The domain of g(x) is all x except 0.
The domain of f(g(x)) consists of all x for which the argument of g is not zero and for which the argument of f is not -3. The argument of g is x so x cannot be zero and the argument of f is g(x) so g(x) cannot be -3. This means that 2/x = -3 is not possible. Solving this for x we find that x cannot be -2/3. The domain of f(g(x)) is therefore all real numbers except -3 and -2/3. The domain of f(f(x)) consists of all x for which the argument of the first f is not -3 and for which the argument of the second f is not -3. The argument of the second f is x so x cannot be -3 and the argument of the first f is f(x) so f(x) cannot be -3. This means that x/(x+3) = -3 is not possible. Solving this for x we find that x cannot be -9/4. The domain of f(f(x)) is therefore all real numbers except -3 and -9/4. The domain of g(f(x)) consists of all x for which the argument of f is not -3 and for which the argument of g is not 0. The argument of f is x so x cannot be -3 and the argument of g is f(x) so f(x) cannot be 0. f(x) is zero if and only if x = 0. The domain of g(f(x)) is therefore all real numbers except -3 and 0. The domain of g(g(x)) consists of all x for which the argument of the first g is not 0 and for which the argument of the second g is not 0. The argument of the second g is x so x cannot be 0 and the argument of the first g is g(x) so g(x) cannot be 0. There is no real number for which g(x) = 2/x is zero. The domain of g(g(x)) is therefore all real numbers except 0. **......!!!!!!!!...................................
RESPONSE --> Oh no! I must have done the wrong problem here!! Let me do this as it is entered here. Okay, f(x) is all x but -3. g(x) is all x except 0. Therefore, f(g(x)) is all x for which the argument of g isn't 0 and of f is not -3. I see this now.
2/x=-3 is not possible because x cannot be -2/3, so in f(g(x)), the domain is all real numbers excluding -3 and -2/3 f(f(x)) is all x where the arguments of the first and second f are not -3. x/(x+3)=-3 is not a possibility, and x can't be -9/4. The domain is all real numbers except -3 and -9/4 g(g(x)) includes all x for which the argument of the first and second g is not 0 The domain of g(g(x) is all real numbers except 0..................................................
......!!!!!!!!...................................
12:40:16 query 5.1.46 (was 3.5.50). f(g(x)) = g(f(x)) = x for x+5 and x-5
Show f(g(x)) = g(f(x)) = x for the given functions.......!!!!!!!!...................................
RESPONSE --> f(g(x))= g(f(x))=x
f(x-5)= x-5+5=x g(f+5)= x+5-5= x.................................................
......!!!!!!!!...................................
12:40:23 ** f(g(x)) = g(x) + 5 = (x-5) + 5 = x.
......!!!!!!!!...................................
RESPONSE --> ok
.................................................
......!!!!!!!!...................................
12:40:28 g(f(x)) = f(x) - 5 = (x+5) - 5 = x. **
......!!!!!!!!...................................
RESPONSE --> ok
.................................................
......!!!!!!!!...................................
12:43:42 query 5.1.53 (was 3.5.60). H(x) = sqrt(x^2 + 1) = f(g(x))
Give the functions f and g such that H is the composite.......!!!!!!!!...................................
RESPONSE --> I think here that f could be sqrt of x and g could be x^2+1 and that would make H(x)= (sqrtx^2+1)
.................................................
......!!!!!!!!...................................
12:44:06 ** The composite f(g(x)) has 'innermost' function g(x), to which the f function is applied.
The 'innermost' function of sqrt(x^2 + 1) is x^2 + 1. The square root is applied to this result. So H(x) = f(g(x)) with f(u) = sqrt(u) and g(x) = x^2 + 1. Thus f(g(x)) = sqrt(g(x)) = sqrt(x^2 + 1). **......!!!!!!!!...................................
RESPONSE --> This is written so complicated but I think I get it.
.................................................
......!!!!!!!!...................................
12:45:38 query 5.1.62 (was 3.5.66). V(r) = 4/3 pi r^2 and r(t) = 2/3 t^3, t>=0.
What is the requested composite function?......!!!!!!!!...................................
RESPONSE --> I have no idea on this one, more word problems
.................................................
......!!!!!!!!...................................
12:47:37 ** V(r(t)) = 4/3 pi * r(t)^2 = 4/3 pi * (2/3 t^3)^2 = 4/3 pi * (4/9 t^6) = 16/27 pi t^6. **
......!!!!!!!!...................................
RESPONSE --> This ended up being far less complicated than I was making it out to be. So I would simply place the value of r(t) into the equation and work it from there.
.................................................
"