SOLUTION: every time i try this problem: {{{dy/dx}}} {{{ 4/cos(x)}}} my answer is undefined

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Question 231658: every time i try this problem: dy%2Fdx +4%2Fcos%28x%29 my answer is undefined
Answer by jsmallt9(3758) About Me  (Show Source):
You can put this solution on YOUR website!
I'm assuming the problem is:
Given: y+=+4%2Fcos%28x%29
Find: dy/dx
If this is not correct then then you'll have to repost your question, being clearer about the problem.

If the equation was
y+=+4%2Fx+=+4x%5E%28-1%29
would you know how to find its derivative? (I hope so because the solution to your problem depends on this.) This is a derivative where you bring the exponent down in front (as a coefficient) and then subtract one from the exponent:
dy%2Fdx+=+%28-1%294x%5E%28%28-1-1%29%29+=+-4x%5E%28-2%29

Of course we don't actually have y+=+4%2Fx, we have y+=+4%2Fcos%28x%29. In a situation like this, where you have a function where it would be nice to just have x, we use the Chain Rule. We find the derivative, treating cos(x) just as if it was x and then we multiply this result by the derivative of cos(x) (which is -sin(x):
y+=+4%28cos%28x%29%29%5E%28-1%29