sin A sin B = ½ cos(A−B) − ½ cos(A+B)
sin70 sin25 = 1/2 [cos45 - cos95]
sin65 sin20 = 1/2 [cos45 - cos85]
sum to get
cos 45 - 1/2 [cos95 + cos85]
cos u + cos v = 2 cos(½(u+v)) cos(½(u−v))
cos95+cos85 = 2cos90 cos5
cos90=0, so we are left with
cos 45 = 1/√2
Evaluate the following with thought the use of a calculator:
Sin70.sin25 + sin65.sin20
And please people explain how you arrived in your answer
Lots of love, timmy
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