f of pi over 6 problem

[jboykin325]

I cannot find the right answer to this problem:

find f(pi/6) if f(x) = [-5cos(9x)/2sin(-x)]

the book says the answer is 0. How do you solve this problem?

[stapel_eliz]

find f(pi/6) if f(x) = [-5cos(9x)/2sin(-x)]

How do you solve this problem?

You evaluate this in the exact same way you've evaluated every other function you've worked with: you plug the argument (in this case, pi/6) in for the variable, and simplify.

[jboykin325]

find f(pi/6) if f(x) = [-5cos(9x)/2sin(-x)]

How do you solve this problem?

You evaluate this in the exact same way you've evaluated every other function you've worked with: you plug the argument (in this case, pi/6) in for the variable, and simplify.

unfortunately, when i plug in pi over 6 for each x, I come out with an answer far from 0, which is the answer from the my worksheet.
it comes out to :

-4.983/-.01828

which does NOT equal zero. :[

[stapel_eliz]

unfortunately, when i plug in pi over 6 for each x, I come out with an answer far from 0....

1) You don't need a calculator for this; do the multiplication inside the cosine, and use the reference-angle value you've memorized.

2) If you're going to use a calculator, make sure you have it set to the correct "mode", or else change the radians to degrees.