SOLUTION: will someone please help me? my question is: how do i find the the given X- value that is a zero of the function? f(x)=x^3+3x^2 -5x+8, x=4 thanks

Algebra ->  Polynomials-and-rational-expressions -> SOLUTION: will someone please help me? my question is: how do i find the the given X- value that is a zero of the function? f(x)=x^3+3x^2 -5x+8, x=4 thanks       Log On


   

Question 111269: will someone please help me?
my question is:
how do i find the the given X- value that is a zero of the function?
f(x)=x^3+3x^2 -5x+8, x=4
thanks
Answer by jim_thompson5910(35256) About Me  (Show Source):
You can put this solution on YOUR website!

f%28x%29=x%5E3%2B3x%5E2-5x%2B8 Start with the given function.


f%284%29=%284%29%5E3%2B3%284%29%5E2-5%284%29%2B8 Plug in x=4. In other words, replace each x with 4.


f%284%29=%2864%29%2B3%284%29%5E2-5%284%29%2B8 Evaluate %284%29%5E3 to get 64.


f%284%29=%2864%29%2B3%2816%29-5%284%29%2B8 Evaluate %284%29%5E2 to get 16.


f%284%29=%2864%29%2B48-5%284%29%2B8 Multiply 3 and 16 to get 48


f%284%29=%2864%29%2B48-20%2B8 Multiply -5 and 4 to get -20


f%284%29=100 Now combine like terms

Since f%284%29%3C%3E0, this means that x=4 is not a zero