2sinA+cosA/sinA-3cosA=-5,求3cos2A+4sin2A的值
问题描述:
2sinA+cosA/sinA-3cosA=-5,求3cos2A+4sin2A的值
答
(2sina+cosa)=-5(sina-3cosa)
7sina=14cosa
sina=2cosa
3cos2a+4sin2a
=6cosacosa-3+8sinacosa
=22cosacosa-3
sinasina+cosacosa=5cosacosa=1
3cos2a+4sin2a
=22cosacosa-3
=7/5