Completing the Square
How to solve quadratic equations by completing the square: example and its solution.
Move the constant term -5 to the right side.
Change +8x to +2⋅x⋅4.
Write +42 on both sides.
Factor the left side by using the formula:
x2 + 2⋅x⋅4 + 42 = (x + 4)2.
Square root both sides.
Add ± in front of √21,
because both (√21)2 and (-√21)2 can be 21.
Move +4 to the right side.
Then x = -4 ± √21.