How do I use the quadratic formula to solve 2 + 5/(r-1) = 12/((r-1)^2)?
1 Answer
Aug 22, 2014
The answers are
You may be tempted to expand
r=y+1
We have an NPV:
2+5/y=12/(y^2)
2y^2+5y=12
2y^2+5y-12=0
y=(-5+-sqrt(5^2-4(2)(-12)))/(2(2))
=(-5+-sqrt(25+96))/4
=(-5+-sqrt(121))/4
=(-5+-11)/4
y=-4,3/2
You may be excited to get an answer and stop, but remember that we used substitution, so substitute back:
r=-3,5/2
This does not conflict with the NPV, so the answer is good.
If you expand, you would have got:
2r^2+r-15=0
Then you would use the quadratic and the answer would be the same.