Question

Find the value of k which is a root of the quadratic equation x^2-2(1+3k)x+7(3+2k)=0 is 7

Answer 1

x²-2(1+3k)x+7(3+2k)=0
given roots is 7, that means x=7

put value of x in quadratic equation,
(7)²-2(1+3k)×7+7(3+2k)=0
49-14(1+3k)+21+14k=0
49-14-42k+21+14k=0
56-28k=0
-28k=-56
k=2

..... hope this helps you...