SOLUTION: Hello I am trying to figure out how to solve quadratic equations. I have X2-8x-9=0

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Question 538112: Hello
I am trying to figure out how to solve quadratic equations. I have X2-8x-9=0
Found 2 solutions by jim_thompson5910, oberobic:
Answer by jim_thompson5910(35256) About Me  (Show Source):
You can put this solution on YOUR website!
x%5E2-8x-9=0 Start with the given equation.


Notice that the quadratic x%5E2-8x-9 is in the form of Ax%5E2%2BBx%2BC where A=1, B=-8, and C=-9


Let's use the quadratic formula to solve for "x":


x+=+%28-B+%2B-+sqrt%28+B%5E2-4AC+%29%29%2F%282A%29 Start with the quadratic formula


x+=+%28-%28-8%29+%2B-+sqrt%28+%28-8%29%5E2-4%281%29%28-9%29+%29%29%2F%282%281%29%29 Plug in A=1, B=-8, and C=-9


x+=+%288+%2B-+sqrt%28+%28-8%29%5E2-4%281%29%28-9%29+%29%29%2F%282%281%29%29 Negate -8 to get 8.


x+=+%288+%2B-+sqrt%28+64-4%281%29%28-9%29+%29%29%2F%282%281%29%29 Square -8 to get 64.


x+=+%288+%2B-+sqrt%28+64--36+%29%29%2F%282%281%29%29 Multiply 4%281%29%28-9%29 to get -36


x+=+%288+%2B-+sqrt%28+64%2B36+%29%29%2F%282%281%29%29 Rewrite sqrt%2864--36%29 as sqrt%2864%2B36%29


x+=+%288+%2B-+sqrt%28+100+%29%29%2F%282%281%29%29 Add 64 to 36 to get 100


x+=+%288+%2B-+sqrt%28+100+%29%29%2F%282%29 Multiply 2 and 1 to get 2.


x+=+%288+%2B-+10%29%2F%282%29 Take the square root of 100 to get 10.


x+=+%288+%2B+10%29%2F%282%29 or x+=+%288+-+10%29%2F%282%29 Break up the expression.


x+=+%2818%29%2F%282%29 or x+=++%28-2%29%2F%282%29 Combine like terms.


x+=+9 or x+=+-1 Simplify.


So the solutions are x+=+9 or x+=+-1


If you need more help, email me at jim_thompson5910@hotmail.com

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Jim


Answer by oberobic(2304) About Me  (Show Source):
You can put this solution on YOUR website!
x^2 -8x -9 = 0
.
So, to factor it you need to find two powers of 9 that have a difference of 1.
-8 = -9+1
.
(x-9)(x+1) = x^2 -8x -9
.
That means x = 9 or -1.
.
%0D%0Agraph%28500%2C500%2C-10%2C10%2C-25%2C25%2Cx%5E2-8%2Ax-9%29%0D%0A
.
Done.