## A community for students. Sign up today

Here's the question you clicked on:

## anonymous 3 years ago Let P(x)=kx^(3)-9x^(2)-15x+50. (a) If 2x+5 is a factor of P(x), find the value of k. (b) Factorize P(x) completely.

• This Question is Closed
1. .Sam.

If 2x+5 is a factor of P(x) Then P(-5/2) = k(-5/2)^(3)-9(-5/2)^(2)-15(-5/2)+50 =0 Find k..

2. .Sam.

You can equate to zero because its a factor of P(x), then -5/2 as value for x

3. anonymous

|dw:1362193274349:dw| |dw:1362193313133:dw|

4. .Sam.

P(-5/2) = k(-5/2)^3+125/4 =0 P(-5/2) = k(-5/2)^3 = -125/4

5. anonymous

|dw:1362193409011:dw|

6. .Sam.

There's something wrong with your calculations, k should be 2

7. anonymous

i know, but i don't know where i wrong

8. anonymous

i know, it should be 75..

9. .Sam.

$-\frac{125}{8}k-\frac{225}{4}+\frac{75}{2}+50=0$ Multiply by 8, $-125k-450+300+400=0 \\ \\ -125k+250=0 \\ \\ k=2$

10. anonymous

i got it

11. anonymous

thanks

#### Ask your own question

Sign Up
Find more explanations on OpenStudy
Privacy Policy