Question

The function f(x) is a quadratic function and the zeros of f(x) are 1 and 5. The y-intercept of f(x) is 20. Write the equation of the quadratic polynomial in standard form.

Answer 1

4x² - 24x + 20 = 0

Explanation:

a(1)² + b(1) + 20 = 0

a(5)² + b(5) + 20 = 0

a + b = - 20 ⇒ b = - a - 20 ...... (1)

25a + 5b = - 20 .......... (2)

(1) -----> (2)

25a + 5( - a - 20) = - 20

20a - 100 = - 20 ⇒ a = 4

4 + b = - 20 ⇒ b = - 24

4x² - 24x + 20 = 0