Find the value of k for which the quadratic equation 9x2 + 3kx + 4 = 0 has equal roots.

Question

Find the value of k for which the quadratic equation 9x² + 3kx + 4 = 0 has equal roots.

Answer 1

Given equation, 9x² + 3kx + 4 = 0

Here, a = 9, b = 3k, c = 4

Now, b² - 4ac = 0

(3k)²- - 4 .9 .4=0

9k² - 144=0

9k²=144

k²=144/9

k²= 16

k²= 4²

k= ± 4

The value of k so that equation 9x²+3kx+4=0 has equal roots is 4 or - 4.