解析 12. (1) 2sin30°⋅cos30°=sin60°,2sin22.5 ° cos 22. 5°=sin45° (2)由(1),可知一个锐角的正弦值与余弦值的积的2倍.等于该角2倍的正弦值.(3) ∵2sin15°⋅cos15°=1/2sin30°=1/2 ∴结论成立.(4) 2sinα⋅cosα=sin2α ...
5-,sin6- 2sin22.5°cos22.5≈2x0.38×0.92≈0.7,sin45°=0.7, 2 .2sin30°.cos30°=sin60°,2sin22.5°.cos22.5=sin45°; (2)由(1)可知,一个角正弦与余弦积的2倍,等于该角2倍的正弦值; (3)2sin159cos15=2x026x0.97=号,sin30=号 故结论成立; (4)2sina.cosa=sin2a...
cos4=0.9975640502598242 cos5=0.9961946980917455 cos6=0.9945218953682733 cos7=0.992546151641322 cos8=0.9902680687415704 cos9=0.9876883405951378 cos10=0.984807753012208 cos11=0.981627183447664 cos12=0.9781476007338057 cos13=0.9743700647852352 cos14=0.9702957262759965 cos15=0.9659258262890683 cos16=0....