How do I prove this trigonometric identity?

Mathematics
Tutor: None Selected Time limit: 1 Day

The farthest I've gotten is converting the left side to 7cos^2x-sinxcosx-4, but I don't know where to go from there.

Aug 9th, 2015

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can u post the original question???




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Aug 9th, 2015

Oops, sorry about that, I thought that popping in an image would let me post text too. I reuploaded the question at https://www.studypool.com/free/229819/how-do-i-prove-this-trigonometric-identity-1

Aug 9th, 2015

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