已知sin(a+π)=5/4且sinacosa<0求2sin(a-π)+3tan(3π-a)/4cos(a-3π)
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已知sin(a+π)=5/4且sinacosa<0求2sin(a-π)+3tan(3π-a)/4cos(a-3π)
已知sin(a+π)=5/4且sinacosa<0求2sin(a-π)+3tan(3π-a)/4cos(a-3π)
已知sin(a+π)=5/4且sinacosa<0求2sin(a-π)+3tan(3π-a)/4cos(a-3π)
sin(a+π)=4/5
-sina=4/5
sina=-4/5
sinacosa<0
那么cosa>0
sin²a+cos²a=1
求得:cosa=3/5
tana=-4/3
2sin(a-π)+3tan(3π-a)/4cos(a-3π)
=-2sina+3tana/4cosa
=8/5+(-4)/(12/15)
=8/5-5
=-17/5
sin(a+π)=4/5
-sina=4/5
sina=-4/5
∵sinacosa<0
∴cosa=3/5
[2sin(a-π)+3tan(3π-a)]/4cos(a-3π)
=(2sina+3tana)/4cosa
代入最后得7/3