SOLUTION: find 3n^2 if n(n+5)=-4

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Question 447108: find 3n^2 if n(n+5)=-4
Answer by chriswen(106) About Me  (Show Source):
You can put this solution on YOUR website!
n(n+5)=-4
n^2+5n=-4
n^2+5n+4=0
Solved by pluggable solver: SOLVE quadratic equation with variable
Quadratic equation an%5E2%2Bbn%2Bc=0 (in our case 1n%5E2%2B5n%2B4+=+0) has the following solutons:

n%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=%285%29%5E2-4%2A1%2A4=9.

Discriminant d=9 is greater than zero. That means that there are two solutions: +x%5B12%5D+=+%28-5%2B-sqrt%28+9+%29%29%2F2%5Ca.

n%5B1%5D+=+%28-%285%29%2Bsqrt%28+9+%29%29%2F2%5C1+=+-1
n%5B2%5D+=+%28-%285%29-sqrt%28+9+%29%29%2F2%5C1+=+-4

Quadratic expression 1n%5E2%2B5n%2B4 can be factored:
1n%5E2%2B5n%2B4+=+1%28n--1%29%2A%28n--4%29
Again, the answer is: -1, -4. Here's your graph:
graph%28+500%2C+500%2C+-10%2C+10%2C+-20%2C+20%2C+1%2Ax%5E2%2B5%2Ax%2B4+%29

Therefore n = -1 or -4.
3n^2= 3 or 48