ANSWERS
a) A = 4x² - 2x - 2
b) if x = -2, A = 18 units²
EXPLANATION
The area of a triangle is the length of the base, multiplied by its height and divided by 2:
[tex]A=\frac{b\cdot h}{2}[/tex]
In this triangle, b = 4x + 2 and h = 2x - 2. The area is:
[tex]A=\frac{(4x+2)(2x-2)}{2}[/tex]
We can simplify this expression. First we have to multiply the binomials in the numerator:
[tex]\begin{gathered} A=\frac{4x\cdot2x-4x\cdot2+2\cdot2x-2\cdot2}{2} \\ A=\frac{8x^2-8x+4x-4}{2} \\ A=\frac{8x^2-4x-4}{2} \end{gathered}[/tex]
Now, using the distributive property for the division:
[tex]\begin{gathered} A=\frac{8x^2}{2}-\frac{4x}{2}-\frac{4}{2} \\ A=4x^2-2x-2 \end{gathered}[/tex]
For part b, we just have to replace x with -2 in the expression above and solve:
[tex]\begin{gathered} A=4(-2)^2-2(-2)-2 \\ A=4\cdot4+4-2 \\ A=16+2 \\ A=18 \end{gathered}[/tex]
