Question

One of the solutions to x2 − 2x − 15 = 0 is x = −3. What is the other solution?

a.x = −5
b.x = −1
c.x = 1
d.x = 5

Answer 1

x2 − 2x − 15 = 0
(x+3)(x-5) = 0
x +3 = 0 so x = -3
x - 5 = 0 so x = 5

answer is d.x = 5

Answer 2

x=5

Explanation:

One of the solutions to
`x^2 - 2x - 15 = 0` is x = −3

To find out the other solution, we factor the x^2-2x-15

Product is -15 and sum is -2

`-5 \cdot 3 = -15`

`-5+3= -2`

So factors are -5 and 3

`x^2 - 2x - 15 = 0`

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

we set each factor =0 and solve for x

`x-5=0, x=5`

`x+3=0, x=-3`

other solution is x=5