Find the roots of the equation x – 72 = - x2 using the quadratic formula.

Question

i need help trying to find the answer please help.

Answer 1

x - 72 = -x²

add x² to both sides

x² + x - 72 = 0

This can be factored

(x+9)(x-8) = 0

x = -9 or x = 8

 

Usng quadratic for ax²+bx+c=0

x = [-b±√(b² - 4ac)]/2a

a=1, b=1, c=-72

 

x = [-1±√(1²-4(1)(-72))]/2(1)

 

x = (-1 ±√289)/2

x = (-1±17)/2

x = 16/2 = 8

or

x= -18/2 = -9

 

As you can see we got the same answer

by either method.