若cota=3 则cos^2a+1/2sin2a的值是多少?
问题描述:
若cota=3 则cos^2a+1/2sin2a的值是多少?
答
cosa/sina=cota=3
cosa=3sina
带入恒等式sin²a+cos²a=1
sin²a=1/10
cos²a=9/10
sin2a=2sinacosa
=2sina(3sina)
=6sin²a
=6/10
所以原式=9/10+1/2×6/10=6/5