设tana=2,则4sina-2cos/5cosa+3sina=;sin^2a+2sinacosa-3cos^2a=
问题描述:
设tana=2,则4sina-2cos/5cosa+3sina=;sin^2a+2sinacosa-3cos^2a=
答
tana=sina/cosa=2
sina=2cosa
sin²a+cos²a=1
5cos²a=1
cos²a=1/5
4sina-2cos/5cosa+3sina
分子分母同除以cosa得:
原式=(4tana-2)/(5+3tana)
=(8-2)/(5+6)
=6/11
sin^2a+2sinacosa-3cos^2a
=4cos²a+4cos²a-3cos²a
=5cos²a
=1