Question

Find all the zeros of the equation.

-4x^4 - 44x^2 + 3600 = 0

A. 5, -5, 6i, -6i
B. 5, -5, 6i, 0
C. -5, -6i

Answer 1

you could say x^2 = y
and replace x^4 with (x^2)^2 = y^2
now solve
-4y^2 -44y+3600=0
I would simplify by dividing all terms by -4 (on both sides of the = sign)
y^2+11y-900=0
now use the quadratic formula to find y or factor (knowing that 25*36= 900)
you get 2 y values. but x= ±sqrt(y), so you get 2 x's for each y, or 4 answers