Solve 3x² + 18x + 15 = 0 by completing the square.

Solution:

If the quadratic expression is of the form ax² + bx + c = 0 then to complete the square we use the result

a{(x + 1/2 of coefficient of x)² + constant term - (1/2 coefficient of x )²}

Given equation is 3x² + 18x + 15 = 0

⇒ 3{ x² + 6x + 5} = 0

⇒ 3 {(x + 3)² + 5 - (3)²}

⇒ 3(x + 3)² - 12 = 0

⇒ 3(x + 3)² = 12

⇒ (x + 3)² = 4

⇒ x + 3 = ± 2

⇒ x + 3 = 2 or x + 3 = -2

⇒ x = -1 or x = -5

Solve 3x² + 18x + 15 = 0 by completing the square.

Summary:

The solutions of 3x² + 18x + 15 = 0 by completing the square method is x = -1 or x = -5