SOLUTION: how do you factor each trinomial completely? -a^2-10a+21 -x^2+9x+20

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Question 272072: how do you factor each trinomial completely?
-a^2-10a+21


-x^2+9x+20
Answer by checkley77(12844) About Me  (Show Source):
You can put this solution on YOUR website!
-a^2-10a+21
a=+%28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%29%2F%282%2Aa%29+
a=(10+-sqrt(-10^2-4*-1*21])/2*-1
a=(10+-sqrt100+84])/-2
a=(10+-sqrt184)/-2
a=(10+-13.56)/-2
a=23.56/-2
a=-11.78 ans.
a=(10-13.56)/-2
a=-3.56/-2
a=1.78 ans.
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-x^2+9x+20
x+=+%28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%29%2F%282%2Aa%29+
x=(-9+-sqrt[9^2-4*-1*20])/2*-1
x=(-9+-sqrt[81+80)/-2
x=(-9+-sqrt161)/-2
x=(-9+-12.69)/-2
x=(-9+12.69)/-2
x=3.69/-2
x=-1.845 ans.
x=(-9-12.69)/-2
x=-21.69/-2
x=10.845 ans.