Because if you did not you would not have a exact answer.
When you solve a proportion, your first step should be to cross-multiply.

=

When you cross-multiply, you should get this equation:
(2x)(3) = (x + 3)(5)
Now, solve it using algebra.
(2x)(3) = (x + 3)(5) Multiply
6x = 5x + 15 Subtract 5x from both sides
x = 15
The value of
x is 15.
Does not exist. The line would be vertical
First plug in (x+h) for x in the function.
f(x+h)= 2(x-h)^2-3(x-h) = 2(x^2-2xh+h^2)-3x-3h =
2x^2-4xh+2h^2-3x-3h - 2x^2 +3x =
(-4xh +2h^2-3h)/h
-4x +2h-3
C = 84 degrees
A = 2B
C = A + 20
A + B + C = 180
A = 2B
A/2 = B
A + (A/2) + (A+20) = 180
multiply each side by 2
2A + A + 2A + 40 = 360
combine like terms
5A + 40 = 360
subtract 40 from both sides
5A = 320
divide both sides by 5
A = 64
C = A + 20
C = 64 + 20
C = 84