# algebra

posted by mary

Use the given zero to find the remaining zeros of the function.
(hx)= 3x^4+5x^3+25x^2+45x-18; zero:-3i

labe

1. Reiny

complex roots always come in conjugate pairs, so we have
x = -3i and x = 3i
two factors are (x + 3i) and (x- 3i)
(x+3i)(x-3i)
= x^2 - 9i^2 = x^2 + 9

Using long algebraic division, you should get
( 3x^4+5x^3+25x^2+45x-18) ÷ (x^2+9)
= 3x^2 + 5x + 2

the quadratic formula can be used to find the other two roots.
btw, it factors

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