Answer:
x = ±20
Step-by-step explanation:
x^2 -1=399
Add 1 to each side
x^2 = 399+1
x^2 = 400
Take the square root of each side
sqrt(x^2) = ±sqrt(400)
-4
-36v+42=186
-36v=144
v=-4
b. 6 cm
Q is the midpoint of PR, so QR = PR/2 = (12 cm)/2 = 6 cm
