Jika parabola y=x²-bx+7 puncaknya mempunyai absis 4 , nilai b

absis dari puncak para bola = -b/2a

y = x^2 -bx + 7
a = 1
b = -b

-b/2a = 4
b/2 = 4
b = 8

Puncak parabola = (absis, ordinat) = (x, y)
absis = x = 4
x = -b/2a
4 = -(-b)/2(1)
4 = b/2
4*2 = b
b = 8

maka pers parabola nya y = x² – 8x + 7