1. anonymous

you mean period?

2. smurfy14

oh yes

3. anonymous

are you looking for the period of $\cos(-.4x)$?

4. smurfy14

yes

5. smurfy14

im looking for something like "it stretches X..."

6. anonymous

period of $\cos(x)$ is $2\pi$ so period of $\cos(bx)$ is $\frac{2\pi}{b}$

7. anonymous

in your case you get $\frac{2\pi}{.4}=5\pi$

8. smurfy14

no heres an example: y=-3cos1/2x has a horizontal stretch of 2 but i cant figure out what it would be for this problem

9. anonymous

so period goes from 2 pi to 5 pi

10. anonymous

oooooooooooooooh silly way to word the problem. in your case $\cos(\frac{1}{2}x)$ teh "stretch" was 2

11. anonymous

in other words the reciprocal of coefficient. the reciprocal of .4 is 5, so stretch is 5

12. smurfy14

ohhhkay so you dont have to include the whole thing like 2/5=5/2 you just take the numerator?