Question

It is given that x=3 is a root of the equation 4x^2 + kx- 15 = 0 , where k is a constant.Find

a) the value of k
b) the other root

Answer 1

Above answer is also correct. Anyways check my attached picture answer.

Thanks !

Answer 2

a) k = -7

b) x = -5/4

Explanation:

`4x^2+kx-15=0`

Substitute
`x=3` and solve for
`k`:

`4(3^2)+3k-15=0\\36+3k-15=0\\3k=-21\implies k=\boxed{-7}`

Plugging
`k` back in to
`4x^2+kx-15=0`:

`4x^2-7k-15=0`

Factor:

`(4x+5)(x-3)=0`

`4x+5=0\implies x=\boxed{-(5)/(4)}`