



 
Hi there. The steps are basically to recall what exact values you know: 0, 30, 45, 60, 90. Then recall that you have trig identities allowing you to use "sum" and "difference", "double" and "half" angles. Cos(15) = Cos(30/2) so I would look for a Cos(θ/2) form. Cos(15) = Cos(30/2) = Sqrt[ (1 + Cos 30) / 2 ] and now I can substitute in the exact value of Cos 30 and simplify. Cos(105) = Cos (90 + 15). So I'd first find a Cos(θ + φ) identity. Cos(105) = Cos(90) Cos(15)  Sin(90) Sin(15) = Sin(15) and then I'd use the same idea to solve Sin(15). This strategy should work for you. Just combine the steps and calculate your question: Sin 105 + Sin 15. Cheers,  


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