tana+b等于负1tana-b等于1/3 sin2a/sin2b为多少

2a=a+b+a-b,2b=(a+b)-(a-b),
∴ sin2a/sin2b
=[sin(a+b)cos(a-b)+cos(a+b)sin(a-b)]/[sin(a+b)cos(a-b)-cos(a+b)sin(a-b)]
分子、分母都除以cos(a+b)cos(a-b),得
[tan(a+b)+tan(a-b)]/[tan(a+b)-tan(a-b)]
=(-1+1/3)/(-1-1/3)
=1/2.

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