The formula of a midpoint:
[tex]\left(\dfrac{x_1+x_2}{2};\ \dfrac{y_1+y_2}{2}\right)[/tex]
D is midpoint of TR.
We have T(-2a, 0) and R(-2b, 2c). Substitute:
[tex]x=\dfrac{-2a+(-2b)}{2}=\dfrac{-2a-2b}{2}=\dfrac{2(-a-b)}{2}=-a-b\\\\y=\dfrac{0+2c}{2}=\dfrac{2C}{2}=c[/tex]
Answer: b. (-a - b, c)
