SOLUTION: how do i solve x^2=11x-80=0 by graphing, and also solveing it using square roots

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Question 174811: how do i solve x^2=11x-80=0 by graphing, and also solveing it using square roots
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Looks like you hit the = sign instead of the + sign
x%5E2+%2B+11x+-+80+=+0 Is this it? If so,
To graph it, make it y+=+x%5E2+%2B+11x+-+80+ and see
where on the graph y=0. I'll do that
+graph%28+500%2C+500%2C+-20%2C+15%2C+-130%2C+24%2C+x%5E2+%2B+11x+-+80%29+
From the graph, it looks like the solutions to
x%5E2+%2B+11x+-+80+=+0 are
x+=+-16 and x+=+5
If these are really the roots, I should be able to say
x+%2B+16+=+0 and
x+-+5+=+0
Now multiplying these together should equal 0 also
%28x+%2B+16%29%28x+-+5%29+=+x%5E2+%2B+11x+-+80
OK
Also, I can use the quadratic formula,
x+=+%28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%29%2F%282%2Aa%29+ , where
a+=+1
b+=+11
c+=+-80
x+=+%28-11+%2B-+sqrt%28+11%5E2-4%2A1%2A%28-80%29+%29%29%2F%282%2A1%29+
x+=+%28-11+%2B-+sqrt%28+121+%2B+320%29%29%2F2+
x+=+%28-11+%2B-+sqrt%28+441+%29%29%2F2+
x+=+%28-11+%2B+21%29%2F2 and
x+=+%28-11+-+21%29%2F2
These work out to
x+=+5
x+=+-16
As they should