How do I solve quadratic equation by completing the square : X^2 - 4X = 5
We have X2 - 4X = 5, write the expression on the left side as X2 - 2•2X = 5. Then we would need extra term 4 to complete the square, so adding 4 on the both sides gives us, X2 - 2•2X + 4 = 5 +4. Simplify further to get: (X-2)2 = 9 , take square root on both sides , X - 2 = ± 3 ⇒ X = 2 ± 3 . Therefore, X = -1 or X = 5 .
