Question

How do you solve `3x^2 + 5x = -x + 4` by completing the square?

Answer 1

y = 3x^2 + 6x - 4 = 3(x^2 + 2x - 4/3) = 0

`[x^2 + 2x - 4/3 = x^2 + 2x + 1 - 1 - 4/3 = 0`

`y = (x + 1)^2 - 7/3 = 0`

`(x + 1)^2 = 7/3` -> `(x + 1 )= +-(sqrt7)/(sqrt3)`

`x = -1 +- (sqrt21/3)`