Find all the zeros of the equation.

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

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

Question

Find all the zeros of the equation.

-4x^4 - 44x^2 + 3600 = 0

A. 5, -5, 6i, -6i	
B. 5, 6i	
C. 5, -5, 6i, 0	
D. -5, -6i

anonymous · Answer

$$-4x^4 - 44x^2 + 3600 = 0$$ divide all by $-4$ get 
$$x^2+11x-900=0$$

anonymous · Answer

sorry i mean get 
$$x^4+11x^2-900=0$$

anonymous · Answer

by some miracle this one actually factors as 
$$(x^2-25)(x^2+36)=0$$ and it should be good to go from there

anonymous · Answer

actually now that i look at it this problem required no work at all
'it is a 4th degree polynomial so it must have 4 zeros
while it is true that some could repeat, if $6i$ is a zero, then its conjugate $-6i$ must also be one
so without any computation we know A is the only possible answer

anonymous · Answer

good to remember if you have to take a test or quiz
if $a+bi$ is a zero of a polynomial with real coefficients, then so is $a-bi$ its conjugate