SOLUTION: Prove that x=2 is a real zero of y=-x^3+7x^2-55x+90

Question 917247: Prove that x=2 is a real zero of y=-x^3+7x^2-55x+90
Found 2 solutions by MathLover1, jim_thompson5910:
Answer by MathLover1(20849) (Show Source): You can put this solution on YOUR website!
factor it first, factor out
............write as and as
...group

...as you can see one of the factors is and if we set it equal to zero we get:
=> which proves that is a real zero of

Answer by jim_thompson5910(35256) (Show Source): You can put this solution on YOUR website!
An alternative easier proof is to plug x = 2 into the equation and evaluate.

y=-x^3+7x^2-55x+90

y=-(2)^3+7(2)^2-55(2)+90

y=0

Since we get a result of y = 0, this means that x = 2 is indeed a root or zero of y=-x^3+7x^2-55x+90

Let me know if you need more help or if you need me to explain a step in more detail.
Feel free to email me at jim_thompson5910@hotmail.com
or you can visit my website here: http://www.freewebs.com/jimthompson5910/home.html

Thanks,

Jim
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