How do you solve m^2+1.8m-1.5=0 by completing the square?

1 Answer
Aug 19, 2017

m= -0.9 + sqrt2.31 and m=-0.9-sqrt2.31

Explanation:

First: (m+0.9)^2 =0
Put m + (half of 1.8) in a bracket and square them

This expands to m^2 +1.8m+0.81. Note that this is almost what we started with - only the c value, 0.81, is wrong. We want it to be -1.5, so we adjust for this by subtracting 0.81 and 1.5

This makes it
(m+0.9)^2 -(0.81+1.5)=0
(m+0.9)^2-2.31=0

Now move the -2.31 to the other side
(m+0.9)^2=2.31

Square root both sides
m+0.9=±sqrt2.31

Move the 0.9 to rhs
m=-0.9±sqrt2.31