Thread: Zeros of polynomials

For some reason this is throwing me off.

Given :

Already found one zero at -1. Book has 3 zeros but given that it's degree 4 shouldn't it have 4 zeros?


And how do I get the complex zeros?

Sorry for having to use pics but i cant figure out the way you all do it yet

Originally Posted by aquavit

For some reason this is throwing me off.

Given :

Already found one zero at -1. Book has 3 zeros but given that it's degree 4 shouldn't it have 4 zeros?


And how do I get the complex zeros?

Sorry for having to use pics but i cant figure out the way you all do it yet

1. Have a look here: http://www.mathhelpforum.com/math-he...-tutorial.html

2. Actually there are 4 zeros if you count the -1 twice. The graph of the function touches the x-axis at x = -1. (In Germany such a case is considered to be a double-zero)

Originally Posted by aquavit

For some reason this is throwing me off.

Given :

Already found one zero at -1. Book has 3 zeros but given that it's degree 4 shouldn't it have 4 zeros?


And how do I get the complex zeros?

Sorry for having to use pics but i cant figure out the way you all do it yet

Using the rational roots theorem you discover that -1 is a root twice.

Using synthetic division, you can factor the original polynomial down to:



Now use the quadratic formula to find your 2 complex roots.

Awesome, i didn't realize -1 was mult.2, now if makes sense Thanks guys!