Use the given zero to find all the zeros of the function. (Enter your answers as a comma-separated list. Include the given zero in your answer.) Function: f(x) = 4x^3 + 5x^2 + 36x + 45 Zero: 3i x =

Question

kinggeorge · Answer

That's $x=3i$ at the end correct?

kinggeorge · Answer

If that's one zero, then so must $x=-3i$. This is a property of complex numbers that's very helpful to memorize.

Now you have $$(x+3i)(x-3i)=x^2+9=0$$Now use long division to find the last zero.

anonymous · Answer

no, 3i is the zero

anonymous · Answer

Function      		
f(x) = 4x3 + 5x2 + 36x + 45 	

zero: 3i

kinggeorge · Answer

Alternatively, you could see a trick, and notice that your final polynomial has a $4x^3$ term and a $+45$ term, and $45/9=5$. So then you could test $4x+5$ and see if $$(4x+5)(x^2+9)=4x^3+5x^2+36x+45$$

kinggeorge · Answer

When I write $x=3i$, it means that $3i$ is a zero for the polynomial.

anonymous · Answer

ah ok