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# Trig identities help watch

1. Hi all - I’m a bit stuck with parts b and c. I’ve got answers for both by simply solving the equations on my Calculator, but I can think of the theory behind it... I’d love to be enlightened...

Question: https://imgur.com/a/1s9hN

Thanks
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3. (Original post by Y11_Maths)
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4. (Original post by JacobPowell)
Hi all - I’m a bit stuck with parts b and c. I’ve got answers for both by simply solving the equations on my Calculator, but I can think of the theory behind it... I’d love to be enlightened...

Question: https://imgur.com/a/1s9hN

Thanks
Few ways to approach part b. One way is to:

0<x<180 so 0<2x<360 hence -35<2x-35<325

Let X=2x-35

Now you’re just solving
cos(X)=0.891 in the region -35<X<325
Then just find x for each X

For last one, divide by cos(x) to obtain an equation entirely in tan(x)

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