SOLUTION: Hi can someone please help me answer this question? thanks so much Describe three ways to determine the zeros of the quadratic function f(x)=-3x^2+27x-42. Solve for the zeros fo

Question 1090512: Hi can someone please help me answer this question? thanks so much
Describe three ways to determine the zeros of the quadratic function f(x)=-3x^2+27x-42. Solve for the zeros for each method.
Found 2 solutions by Fombitz, Boreal:
Answer by Fombitz(32388) (Show Source): You can put this solution on YOUR website!
Graphically,
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Factoring,

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Completing the square,

So,

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Answer by Boreal(15235) (Show Source): You can put this solution on YOUR website!
f(x)=-3x^2+27x-42.
factor -3(x^2-9x+14)=-3(x-7)(x-2)=0, and x=7, 2
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complete the square after first changing all signs to 3x^2-27x+42=0 and move the constant so that 3x^2-27x=-42
divide the left side by 3 to get 3(x^2-9x) and complete the square by taking half of -9 and squaring it to get 20.25; X^2-9X+20.25=-42+3(20.25)
add 60.75 to the right because of the 3
now it is 3(x-4.5)^2=18.75
Divide by 3
(x-4.5)^2=6.25
take the square root.
x-4.5=+/- 2.5
x=7, 2
===========================
graph it

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