已知:cos2a 除以 sin(a-pai/4) = 负的2分支根号2 求:cosa + sina =多少?A:负的2分支根号7 B:-1/2C:1/2 D:2分支根号7
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![已知:cos2a 除以 sin(a-pai/4) = 负的2分支根号2 求:cosa + sina =多少?A:负的2分支根号7 B:-1/2C:1/2 D:2分支根号7](/uploads/image/z/2667188-20-8.jpg?t=%E5%B7%B2%E7%9F%A5%EF%BC%9Acos2a+%E9%99%A4%E4%BB%A5+sin%28a-pai%2F4%29+%EF%BC%9D+%E8%B4%9F%E7%9A%842%E5%88%86%E6%94%AF%E6%A0%B9%E5%8F%B72+%E6%B1%82%EF%BC%9Acosa+%2B+sina+%3D%E5%A4%9A%E5%B0%91%3FA%EF%BC%9A%E8%B4%9F%E7%9A%842%E5%88%86%E6%94%AF%E6%A0%B9%E5%8F%B77+B%EF%BC%9A%EF%BC%8D1%2F2C%EF%BC%9A1%2F2+D%EF%BC%9A2%E5%88%86%E6%94%AF%E6%A0%B9%E5%8F%B77)
已知:cos2a 除以 sin(a-pai/4) = 负的2分支根号2 求:cosa + sina =多少?A:负的2分支根号7 B:-1/2C:1/2 D:2分支根号7
已知:cos2a 除以 sin(a-pai/4) = 负的2分支根号2 求:cosa + sina =多少?
A:负的2分支根号7 B:-1/2
C:1/2 D:2分支根号7
已知:cos2a 除以 sin(a-pai/4) = 负的2分支根号2 求:cosa + sina =多少?A:负的2分支根号7 B:-1/2C:1/2 D:2分支根号7
cos2a=cosa^2-sina^2=(cosa+sina)*(cosa-sina)
sin(a-π/4)=sina*cos(π/4)-cosa*sin(π/4)=√2(sina-cosa)/2
cos2a 除以 sin(a-pai/4) = 负的2分支根号2
即:(cosa+sina)*(cosa-sina)/[√2(sina-cosa)/2]=-√2/2
故cosa+sina=1/2
选C
哦,cos(2*a)/sin(a-pi/4)=-sin(2*a-pi/2)/sin(a-pi/4)=-2cos(a-pi/4)=-2^-0.5;
所以: cos(a)+sin(a)=2^0.5*cos(a-pi/4)=-2^-0.5*2^0.5/2=1/2;