For what value of k the quadratic equation 9x2- kx + 81 = 0 has equal roots

Question

Find the value of k for which the quadratic equation 9x²-kx+81=0 has equal roots.

Answer 1

Given equation, 9x²-kx+81=0

Now, b² - 4ac = 0

(-k)² - 4 .9 .81=0

k² - 2916=0

k² = 2916

k² = (54)²

k= ± 54

The value of k so that the equation 9x²-kx+81=0 has equal roots is 54 or -54.