## anonymous one year ago Which of the following would best represent a cosine function with an amplitude of 3, a period of pi over 2, and a midline at y = −4? f(x) = −4 cos 4x + 3 f(x) = 3 cos(x − pi over 2) − 4 f(x) = 4 cos(x − pi over 2) + 3 f(x) = 3 cos 4x − 4

1. anonymous

2. anonymous

The amplitude is the number before the trig function (sine, cosine, etc.). So we want a 3 before the cos in this case.

3. anonymous

ok

4. anonymous

can u help

5. anonymous

It will usually be written out like this $\large acos(bx-c)+d\\\large amplitude~=~a\\\\\large period~=~\frac{2pi}{b}$

6. anonymous

The midline is the point halfway between the top and bottom of the wave. The midline of a cos function is usually 0. So to change it to 4 smaller, we have to make the vertical change (the d in my example) equal -4. So set d=-4

7. anonymous

A

8. anonymous

Wrong. Did you just guess?

9. anonymous

No

10. anonymous

Nevermind i figured it out thanks anyways

11. anonymous

$\large amplitude=a\\\large amplitude=3\\\large a=3$ So in $$\large acos(bx)+d$$, $$\large a=3$$

12. anonymous

So did you get the answer then?