completing the square

Step-by-step explanation:

5x² - 15x - 4 = 0

Add 4 to both sides.

5x² - 15x = 4

The coefficient of 5x² is 5, divide both sides by 5.

x² - 3x = 4/5

The coefficient of -3x is -3. Let b=-3.

Then we need to add (b/2)^2=9/4 to both sides to complete the square.

Add 9/4 to both sides.

x² - 3x + 9/4 = 61/20

Factor left side.

(x-3/2)² = 61/20

Take square root of both sides.

x-3/2 = ± √(61/20)

Add 3/2 to both sides.

x = 3/2 ± √(61/20)