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# Core 3 trig and functions watch

1. I'm really struggling to rearrange trig equations. How would I prove the following:

(4cos2x)/(1+ cos2x) = 4-2sec^2x.

I get the 2sec^2x using 1/cosx= secx but I don't know which step I'm getting wrong.

Also, functions, there is one question which I don't understand at all. If f(x) is root(mx + 7) -4, explain how it can be deduced that neither this function or its inverse meet the line y=x, and determine the set of possible values of m. Having worked through the answer with the mark scheme, I don't understand why f(x) is equated to x, to work out the quadratic equation which gets m.

Not sure how much of that makes sense, but any help would be great
2. Not sure on first part but second is simply this

You want to find out if f(x) hits the line y = x, therefore for this to be the case f(x) = x at the point where they meet. This is why the markscheme sets f(x) = x to work out the equation!
Not sure on first part but second is simply this

You want to find out if f(x) hits the line y = x, therefore for this to be the case f(x) = x at the point where they meet. This is why the markscheme sets f(x) = x to work out the equation!
Thank you I worked out the trig bit in the end, just made a mistake with my rearranging.
4. (Original post by definite_maybe)
Thank you I worked out the trig bit in the end, just made a mistake with my rearranging.
could you explain how you did the trig question? I can't seem to do it!

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