Question

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

Answer 1

Answer:

a) k = -7

b) x = -5/4

Step-by-step 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:

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

$4x+5=0\implies x=\boxed{-\frac{5}{4}}$

Answer 2

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

Thanks !