12.
Solve by completing the square.
1. Divide both sides by the coefficient of the square term.
2. Transpose known terms to one side and unknown terms to the other. A term is an unknown term if it has a factor of the unknown x in it and it is a know term if it doesn't.
3. Add the square of half the coefficient of the first degree term to both sides. The coefficient of the first degree term is 1/2. Half of that is 1/4. The square of that is 1/16. We add 1/16 to both sides.
On the right we are adding fractions, so we need common denominators. The common denominator is 16. We need to multiply both the top and bottom of the 5 by 16.
4. Simplify
5. Take square roots of both sides.
6. Add 1/4 to both sides
This gives 2 answers
or
which are the two answers we got by factoring. To see the checks, see the discussion of solving this problem by factoring.