I Need A Little Help Understanding Pre Calculus, Please!?

Emperor Penguin

New member
[a] Find the value of tan (?–?) if cos ? = 3/5, sin ? = 5/13, 0° < ? < 90°, and 0° < ? < 90°.

If cos ? = 0.8 and 0° < ? < 90°, find the exact value of sin 2?.

Having trouble understanding these.
 
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