D) construction of the angle bisector.
So if you have a triangle that is not equilateral the perpendicular bisectors would not work so you need angle bisectors.
I have drawn a diagram
The green is the angle bisectors and the yellow the perpendicular bisectors.
You can see the problem straight away
F(x)=2(x+10)=24
2(x+10)=24
divide 2
x+10=12
minus 10
x=2
D
Answer: x = -1 y = 4 I got my answer by solving for one variable in the first equation and then substituting what I got for that variable into the second equation in place of that aforementioned variable then solving for the last variable.
SU would be the hypotenuse so you can use Pythagorean Theorem to solve this problem.
42^2 + 56^2 = c^2
1764 + 3136 = c^2
4900 = c^2
70 = c