Problem 1
Answer: Choice A. (0,9)
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Explanation:
The first task is to determine the function for f(x). Because it's linear, it's in the form y = mx+b. Let's find the slope m.
Select any two columns to pick out (x,y) points from the f(x) function. I'll pick the first two columns to select the points (-6,15) and (-4,11). Apply the slope formula to these two points to get...
m = (y2-y1)/(x2-x1)
m = (11-15)/(-4-(-6))
m = (11-15)/(-4+6)
m = -4/2
m = -2
Then use this m value along with any of the points of the table to determine the y intercept b. I'll use the point (-6,15)
y = mx+b
b = y-mx
b = 15-(-2)*(-6)
b = 15-12
b = 3
The y = mx+b equation becomes y = -2x+3 and that leads directly to the function f(x) = -2x+3.
Repeat all of those steps but do so for g(x) this time. I'll skip those steps over but you should get the function g(x) = 5x-6.
The y intercepts of f(x) and g(x) found were 3 and -6 respectively. Subtract those values to find the y intercept of h(x) = (f-g)(x) = f(x)-g(x).
So we get 3-(-6) = 3+6 = 9 which leads to the location (0, 9).
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Problem 2
Answer: Choice A
x is any real number but x cannot equal -2, -1 or 1.
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Explanation:
Through trial and error, the factor by grouping method, or using your graphing calculator, factor the denominator to get
g(x) = x^3+2x^2-x-2 = (x+2)(x+1)(x-1)
The factors (x+2), (x+1) and (x-1) lead to the roots of x = -2, x = -1, and x = 1 in that order. Those three roots of g(x) will make g(x) = 0 and cause a division by zero error in the denominator. So we must kick out those three values from the domain. Every other real number is allowed in the domain. So that's how we get the notation for choice A. It starts off saying x is a real number. Then it goes onto say that -2, -1 and 1 aren't allowed.
So overall the domain is described as: "x can be almost any real number except x cannot be -2, cannot be -1, and it cannot be 1".
Side note: We don't involve the numerator function at all.
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Problem 3
Answer: Choice B.
2x+1 and x-3
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Explanation:
The height is x, which we can factor out like this
2x^3-5x^2-3x
2x^2*x - 5x*x - 3*x
x(2x^2-5x-3)
Effectively you would use the distribution rule in reverse.
Now let's factor the remaining expression in the parenthesis.
I'll use the factor by grouping method.
2x^2-5x-3
2x^2-6x+1x-3
(2x^2-6x) + (1x-3)
2x(x-3) + 1(x-3)
(2x+1)(x-3)
Therefore, the full factorization is
x(2x+1)(x-3)
which shows we have the dimensions of x, (2x+1) and (x-3). The order doesn't matter so we could easily have (2x+1) the length and (x-3) the width, or we could have it the other way around.
You can verify that (2x+1)(x-3) expands out to 2x^2-5x-3 using either the FOIL method or the box method.
