Question

If one root of the quadratic equation x2 - 11x + k = 0 is 9 find the value of k

Answer 1

Here's the solution:
$p(x) = x^{2} - 11x + k \\ since \: 9 \: is \: a \: root \\ p(9) = 0 \\ p(9) = {9}^{2} - 99 + k \\ 81 - 99 + k = 0 \\ k = 18$

Answer 2

Answer:

Step-by-step explanation:

let the other root be y

therefore two roots will be 9 and y

as the roots sum should be equal to - b/a

therefore 9 + y= -(-11)/1

therefore y = 2

and also the product of roots is equal to c/a

therefore (9)(2) = k/1

therefore k = 18