SOLUTION: find the value of x to 3 d.p when: x^2 + 20x = 400cm^2

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Question 459676: find the value of x to 3 d.p when:
x^2 + 20x = 400cm^2
Answer by Alan3354(69443) About Me  (Show Source):
You can put this solution on YOUR website!
x^2 + 20x = 400cm^2
Units aren't usual in a quadratic.
x^2 + 20x - 400 = 0
Solved by pluggable solver: SOLVE quadratic equation (work shown, graph etc)
Quadratic equation ax%5E2%2Bbx%2Bc=0 (in our case 1x%5E2%2B20x%2B-400+=+0) has the following solutons:

x%5B12%5D+=+%28b%2B-sqrt%28+b%5E2-4ac+%29%29%2F2%5Ca

For these solutions to exist, the discriminant b%5E2-4ac should not be a negative number.

First, we need to compute the discriminant b%5E2-4ac: b%5E2-4ac=%2820%29%5E2-4%2A1%2A-400=2000.

Discriminant d=2000 is greater than zero. That means that there are two solutions: +x%5B12%5D+=+%28-20%2B-sqrt%28+2000+%29%29%2F2%5Ca.

x%5B1%5D+=+%28-%2820%29%2Bsqrt%28+2000+%29%29%2F2%5C1+=+12.3606797749979
x%5B2%5D+=+%28-%2820%29-sqrt%28+2000+%29%29%2F2%5C1+=+-32.3606797749979

Quadratic expression 1x%5E2%2B20x%2B-400 can be factored:
1x%5E2%2B20x%2B-400+=+%28x-12.3606797749979%29%2A%28x--32.3606797749979%29
Again, the answer is: 12.3606797749979, -32.3606797749979. Here's your graph:
graph%28+500%2C+500%2C+-10%2C+10%2C+-20%2C+20%2C+1%2Ax%5E2%2B20%2Ax%2B-400+%29

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x = 12.36 cm
x = -32.36 cm
Good luck with the -32 cm