SOLUTION: Hello. I'm checking to see if I did this problem correctly using the quadratic formula y^2 - 18y = -81 thanks!

Algebra ->  Equations -> SOLUTION: Hello. I'm checking to see if I did this problem correctly using the quadratic formula y^2 - 18y = -81 thanks!      Log On


   

Question 190115: Hello.
I'm checking to see if I did this problem correctly using the quadratic formula
y^2 - 18y = -81
thanks!
Answer by jim_thompson5910(35256) About Me  (Show Source):
You can put this solution on YOUR website!

y%5E2-18y=-81 Start with the given equation.


y%5E2-18y%2B81=0 Add 81 to both sides.


Notice we have a quadratic equation in the form of ay%5E2%2Bby%2Bc where a=1, b=-18, and c=81


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-%28-18%29+%2B-+sqrt%28+%28-18%29%5E2-4%281%29%2881%29+%29%29%2F%282%281%29%29 Plug in a=1, b=-18, and c=81


y+=+%2818+%2B-+sqrt%28+%28-18%29%5E2-4%281%29%2881%29+%29%29%2F%282%281%29%29 Negate -18 to get 18.


y+=+%2818+%2B-+sqrt%28+324-4%281%29%2881%29+%29%29%2F%282%281%29%29 Square -18 to get 324.


y+=+%2818+%2B-+sqrt%28+324-324+%29%29%2F%282%281%29%29 Multiply 4%281%29%2881%29 to get 324


y+=+%2818+%2B-+sqrt%28+0+%29%29%2F%282%281%29%29 Subtract 324 from 324 to get 0


y+=+%2818+%2B-+sqrt%28+0+%29%29%2F%282%29 Multiply 2 and 1 to get 2.


y+=+%2818+%2B-+0%29%2F%282%29 Take the square root of 0 to get 0.


y+=+%2818+%2B+0%29%2F%282%29 or y+=+%2818+-+0%29%2F%282%29 Break up the expression.


y+=+%2818%29%2F%282%29 or y+=++%2818%29%2F%282%29 Combine like terms.


y+=+9 or y+=+9 Simplify.


So the answer is y+=+9