三角恒等变换的题,6,7,8.能做几道做几道.
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三角恒等变换的题,6,7,8.能做几道做几道.
三角恒等变换的题,6,7,8.能做几道做几道.
三角恒等变换的题,6,7,8.能做几道做几道.
6 tan(α+π/4)=tan(α+B-B+π/4)
=[tan(α+B)-tan(B-π/4)]/(1+tan(α+B)tan(B-π/4)
=3/22
C正确
7 cosα=2√5/5
sinB=√10/10
sin(a+B)=sinacosB+sinbcosa
=√5/5x3√10/10+√10/10x2√5/5
=√2/2
a+b=π/4或3π/4
C正确
8
cos(a-π/6)+sina=cosacosπ/6+sinasinπ/6+sina
=(√3/2)cosa+(3/2)sina=4√3/5
∴(1/2)cosa+(√3/2)sina=4/5
sin(x+7π/6)=sinacos7π/6+sin7π/6cosa
=(-√3/2)sina+(-1/2)cosa=-4/5
C正确
所以答案CCC