已知p/2
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已知p/2已知p/2已知p/2π/20πsin2a=sin[(a+b)+(a-b)]=sin(a+b)cos(a-b)+cos(a+b)sin(a-b)=-3/5*12/13-4/5*5/13=-56
已知p/2 已知p/2 sin2a=sin[(a+b)+(a-b)] 全部展开 sin2a=sin[(a+b)+(a-b)] 收起
已知p/2
π/2
=sin(a+b)cos(a-b)+cos(a+b)sin(a-b)
= -3/5 *12/13 -4/5 * 5/13
= - 56/65
=sin(a+b)cos(a-b)+sin(a-b)cos(a+b)
cos(a-b)=12/13
p/2
sin(a-b)=√[1-(12/13)^2]
=5/13
p/2
=sin(a+b)cos(a-b)+sin(a-b)cos(a+b)
cos(a-b)=12/13
p/2
sin(a-b)=√[1-(12/13)^2]
=5/13
p/2
=-√[1-(-3/5)^2]
=-4/5
sin2a=(-3/5)*(12/13)+(5/13)*(-4/5)
=(-36-20)/65=-56/65