Answer:
The solution of the equation are 3 , -11
Step-by-step explanation:
* Lets revise how to make the completing square
- The form of the completing square is a(x - h)² + k, where a , h , k
are constant
- The general form of the quadratic is ax² + bx + c, where a , b , c
are constant
- To change the general form to the completing square form equate
them and find the constant a , h , k
* Now lets solve the problem
∵ x² + 8x = 33 ⇒ subtract 33 from both sides
∴ x² + 8x - 33 = 0
- lets change the general form to the completing square
∴ x² + 8x - 33 = a(x - h)² + k ⇒ solve the bracket of power 2
∴ x² + 8x - 33 = a(x² - 2hx + h²) + k ⇒ multiply the bracket by a
∴ x² + 8x - 33 = ax² - 2ahx + ah² + k ⇒ compare the two sides
∵ x² = ax² ⇒ ÷ x²
∴ a = 1
∴ -2ah = 8 ⇒ substitute the value of a
∴ -2(1)h = 8 ⇒ -2h = 8 ⇒ ÷ (-2)
∴ h = -4
∵ ah² + k = -33 ⇒ substitute the value of a and h
∴ (1)(-4)² + k = -33
∴ 16 + k = -33 ⇒ subtract 16 from both sides
∴ k = -49
∴ x² + 8x - 33 = (x + 4)² - 49
* Now lets solve the completing square
∵ (x + 4)² - 49 = 0 ⇒ add 49 to both sides
∴ (x + 4)² = 49 ⇒ take square root for both sides
∴ (x + 4) = ± 7
∵ x + 4 = 7 ⇒ subtract 4 from both sides
∴ x = 3
∵ x + 4 = -7 ⇒ subtract 4 from both sides
∴ x = -11
* The solution of the equation are 3 , -11
