Determine the equation whose roots are –1, –5, and –3.
A x3 + 9x2 + 23x + 15 = 0

B x3 – x2 + 17x + 15 = 0
C x3 – 13x + 15 = 0
D x3 – 9x2 – 15 = 0

Question

Determine the equation whose roots are –1, –5, and –3. 
A x3 + 9x2 + 23x + 15 = 0

B x3 – x2 + 17x + 15 = 0
C x3 – 13x + 15 = 0
D x3 – 9x2 – 15 = 0

anonymous · Answer

(x + 1)(x + 5)(x + 3) = 0    multiply out.

anonymous · Answer

A quick shortcut for timed tests is to realize that all terms are going to be positive.  Only one answer has all positive terms.

anonymous · Answer

so the answer is a?

anonymous · Answer

Yes, that's the short-cut, but for practice, you really should multiply it all out.  What if the question in the future is not multiple-choice?

anonymous · Answer

So the learning points here are the equation I gave you (how to set that up on your own) and how to multiply it out.