4x^2+12x=7

Question

Solve by completing square

Answer 1

Divide both sides by 4:   x² + 3x = 7/4

 

Take half of 3, square that number and add it to both sides:

 

     (3/2)² = 9/4

 

     x² + 3x + 9/4 = 7/4 + 9/4 = 4

 

Factor the left side:  (x + 3/2)² = 4

 

 

 

Take square roots of both sides and solve for x:

 

     x + 3/2 = ± √4 = ± 2

 

            x = -3/2 ± 2 = 1/2, -7/2