SOLUTION: Please help solve: y^2-9y-10=0

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Question 627057: Please help solve: y^2-9y-10=0
Answer by jim_thompson5910(35256) About Me  (Show Source):
You can put this solution on YOUR website!

y%5E2-9y-10=0 Start with the given equation.


Notice that the quadratic y%5E2-9y-10 is in the form of Ay%5E2%2BBy%2BC where A=1, B=-9, and C=-10


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


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


y+=+%28-%28-9%29+%2B-+sqrt%28+%28-9%29%5E2-4%281%29%28-10%29+%29%29%2F%282%281%29%29 Plug in A=1, B=-9, and C=-10


y+=+%289+%2B-+sqrt%28+%28-9%29%5E2-4%281%29%28-10%29+%29%29%2F%282%281%29%29 Negate -9 to get 9.


y+=+%289+%2B-+sqrt%28+81-4%281%29%28-10%29+%29%29%2F%282%281%29%29 Square -9 to get 81.


y+=+%289+%2B-+sqrt%28+81--40+%29%29%2F%282%281%29%29 Multiply 4%281%29%28-10%29 to get -40


y+=+%289+%2B-+sqrt%28+81%2B40+%29%29%2F%282%281%29%29 Rewrite sqrt%2881--40%29 as sqrt%2881%2B40%29


y+=+%289+%2B-+sqrt%28+121+%29%29%2F%282%281%29%29 Add 81 to 40 to get 121


y+=+%289+%2B-+sqrt%28+121+%29%29%2F%282%29 Multiply 2 and 1 to get 2.


y+=+%289+%2B-+11%29%2F%282%29 Take the square root of 121 to get 11.


y+=+%289+%2B+11%29%2F%282%29 or y+=+%289+-+11%29%2F%282%29 Break up the expression.


y+=+%2820%29%2F%282%29 or y+=++%28-2%29%2F%282%29 Combine like terms.


y+=+10 or y+=+-1 Simplify.


So the solutions are y+=+10 or y+=+-1


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