SOLUTION: r squared plus 3r equals 8

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Question 316931: r squared plus 3r equals 8
Found 2 solutions by tinbar, JBarnum:
Answer by tinbar(133) About Me  (Show Source):
You can put this solution on YOUR website!
r^2+3r=8
r^2+3r-8=0
use quadratic formula to solve

Answer by JBarnum(2146) About Me  (Show Source):
You can put this solution on YOUR website!
Solved by pluggable solver: SOLVE quadratic equation with variable
Quadratic equation ar%5E2%2Bbr%2Bc=0 (in our case 1r%5E2%2B3r%2B-8+=+0) has the following solutons:

r%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=%283%29%5E2-4%2A1%2A-8=41.

Discriminant d=41 is greater than zero. That means that there are two solutions: +x%5B12%5D+=+%28-3%2B-sqrt%28+41+%29%29%2F2%5Ca.

r%5B1%5D+=+%28-%283%29%2Bsqrt%28+41+%29%29%2F2%5C1+=+1.70156211871642
r%5B2%5D+=+%28-%283%29-sqrt%28+41+%29%29%2F2%5C1+=+-4.70156211871642

Quadratic expression 1r%5E2%2B3r%2B-8 can be factored:
1r%5E2%2B3r%2B-8+=+1%28r-1.70156211871642%29%2A%28r--4.70156211871642%29
Again, the answer is: 1.70156211871642, -4.70156211871642. Here's your graph:
graph%28+500%2C+500%2C+-10%2C+10%2C+-20%2C+20%2C+1%2Ax%5E2%2B3%2Ax%2B-8+%29