SOLUTION: When working on finding the zeros on f(x)=x(x2-8x-2) how do I even start? I"m very lost. I have look at the examples given in my text book, but can't make sense of it.

Algebra ->  Polynomials-and-rational-expressions -> SOLUTION: When working on finding the zeros on f(x)=x(x2-8x-2) how do I even start? I"m very lost. I have look at the examples given in my text book, but can't make sense of it.      Log On


   



Question 305990: When working on finding the zeros on f(x)=x(x2-8x-2) how do I even start? I"m very lost. I have look at the examples given in my text book, but can't make sense of it.
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
f%28x%29+=+x%2A%28x%5E2+-+8x+-+2%29
What values of x make f%28x%29+=+0 ?
One solution is obviously x+=+0
because f%280%29+=+0%2A%28-2%29+=+0
Then find the zeros of
x%5E2+-+8x+-+2+=+0
I'll solve by completing the square
x%5E2+-+8x+%2B+%288%2F2%29%5E2+=+%288%2F2%29%5E2+%2B+2
x%5E2+-+8x+%2B+16+=+16+%2B+2
%28x+-+4%29%5E2+=+18
x+-+4+=+sqrt%2818%29
x+-+4+=+3%2Asqrt%282%29
x+=+4+%2B-+3%2Asqrt%282%29
It looks like the zeros are:
x+=+0
x+=+4+%2B+3%2Asqrt%282%29
x+=+4+-+3%2Asqrt%282%29