SOLUTION: Can someone please help solve for r? r=__ r^2+3*r=8

Algebra ->  Quadratic Equations and Parabolas  -> Quadratic Equations Lessons  -> Quadratic Equation Lesson -> SOLUTION: Can someone please help solve for r? r=__ r^2+3*r=8      Log On


   

Question 407298: Can someone please help solve for r?
r=__
r^2+3*r=8
Answer by jim_thompson5910(35256) About Me  (Show Source):
You can put this solution on YOUR website!
r%5E2%2B3r=8 Start with the given equation.


r%5E2%2B3r-8=0 Subtract 8 from both sides.


Notice we have a quadratic equation in the form of ar%5E2%2Bbr%2Bc where a=1, b=3, and c=-8


Let's use the quadratic formula to solve for r


r+=+%28-b+%2B-+sqrt%28+b%5E2-4ac+%29%29%2F%282a%29 Start with the quadratic formula


r+=+%28-%283%29+%2B-+sqrt%28+%283%29%5E2-4%281%29%28-8%29+%29%29%2F%282%281%29%29 Plug in a=1, b=3, and c=-8


r+=+%28-3+%2B-+sqrt%28+9-4%281%29%28-8%29+%29%29%2F%282%281%29%29 Square 3 to get 9.


r+=+%28-3+%2B-+sqrt%28+9--32+%29%29%2F%282%281%29%29 Multiply 4%281%29%28-8%29 to get -32


r+=+%28-3+%2B-+sqrt%28+9%2B32+%29%29%2F%282%281%29%29 Rewrite sqrt%289--32%29 as sqrt%289%2B32%29


r+=+%28-3+%2B-+sqrt%28+41+%29%29%2F%282%281%29%29 Add 9 to 32 to get 41


r+=+%28-3+%2B-+sqrt%28+41+%29%29%2F%282%29 Multiply 2 and 1 to get 2.


r+=+%28-3%2Bsqrt%2841%29%29%2F%282%29 or r+=+%28-3-sqrt%2841%29%29%2F%282%29 Break up the expression.


So the answers are r+=+%28-3%2Bsqrt%2841%29%29%2F%282%29 or r+=+%28-3-sqrt%2841%29%29%2F%282%29


If you need more help, email me at jim_thompson5910@hotmail.com

Also, please consider visiting my website: http://www.freewebs.com/jimthompson5910/home.html and making a donation. Thank you

Jim