Question

If one zero of the quadratic polynomial (k + 3) x2 + kx + 3 is −2 find k

Answer 1

Answer : k = -15/2

GIVEN :

Quadratic Polynomial = (k + 3) x2 + kx + 3

Zero of the quadratic polynomial = -2

Substitute (-2) in the polynomial.

(k + 3) (-2)² + k(-2) + 3 = 0

(k + 3 ) (4) - 2k + 3 = 0

4k + 12 - 2k + 3 = 0

4k + 12 - 2k + 3 = 0

2k + 15 = 0

2k = -15

k = -15/2

Therefore, the value of k is -15/2

Answer 2

Given: Quadratic polynomial - (k + 3) x^2 + kx + 3 and one of its zeroes is (-2).

To find: The value of k.

Answer:

Let p(x) be equal to (k + 3) x2 + kx + 3.

Finding p(x) when x = -2,

p(-2) = (k + 3) x^2 + kx + 3

= (k + 3)*(-2)^2 + k*(-2) + 3

= (k + 3)*4 - 2k + 3

= 4k + 12 - 2k + 3

= 2k + 15

Equating the above result to 0,

2k + 15 = 0

2k = -15

k = -15/2.