己知cos(兀/4一a)=3/5,sin(5兀/4十b)=-12/13,a属于(兀/4,3兀/4),b属于(O,兀/4).求sin(a+...己知cos(兀/4一a)=3/5,sin(5兀/4十b)=-12/13,a属于(兀/4,3兀/4),b属于(O,兀/4).求sin(a+b)的值
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![己知cos(兀/4一a)=3/5,sin(5兀/4十b)=-12/13,a属于(兀/4,3兀/4),b属于(O,兀/4).求sin(a+...己知cos(兀/4一a)=3/5,sin(5兀/4十b)=-12/13,a属于(兀/4,3兀/4),b属于(O,兀/4).求sin(a+b)的值](/uploads/image/z/1063655-71-5.jpg?t=%E5%B7%B1%E7%9F%A5cos%EF%BC%88%E5%85%80%2F4%E4%B8%80a%EF%BC%89%3D3%2F5%2Csin%EF%BC%885%E5%85%80%2F4%E5%8D%81b%EF%BC%89%3D-12%2F13%2Ca%E5%B1%9E%E4%BA%8E%EF%BC%88%E5%85%80%2F4%2C3%E5%85%80%2F4%EF%BC%89%2Cb%E5%B1%9E%E4%BA%8E%EF%BC%88O%2C%E5%85%80%2F4%EF%BC%89.%E6%B1%82sin%EF%BC%88a%2B...%E5%B7%B1%E7%9F%A5cos%EF%BC%88%E5%85%80%2F4%E4%B8%80a%EF%BC%89%3D3%2F5%2Csin%EF%BC%885%E5%85%80%2F4%E5%8D%81b%EF%BC%89%3D-12%2F13%2Ca%E5%B1%9E%E4%BA%8E%EF%BC%88%E5%85%80%2F4%2C3%E5%85%80%2F4%EF%BC%89%2Cb%E5%B1%9E%E4%BA%8E%EF%BC%88O%2C%E5%85%80%2F4%EF%BC%89.%E6%B1%82sin%EF%BC%88a%2Bb%EF%BC%89%E7%9A%84%E5%80%BC)
己知cos(兀/4一a)=3/5,sin(5兀/4十b)=-12/13,a属于(兀/4,3兀/4),b属于(O,兀/4).求sin(a+...己知cos(兀/4一a)=3/5,sin(5兀/4十b)=-12/13,a属于(兀/4,3兀/4),b属于(O,兀/4).求sin(a+b)的值
己知cos(兀/4一a)=3/5,sin(5兀/4十b)=-12/13,a属于(兀/4,3兀/4),b属于(O,兀/4).求sin(a+...
己知cos(兀/4一a)=3/5,sin(5兀/4十b)=-12/13,a属于(兀/4,3兀/4),b属于(O,兀/4).求sin(a+b)的值
己知cos(兀/4一a)=3/5,sin(5兀/4十b)=-12/13,a属于(兀/4,3兀/4),b属于(O,兀/4).求sin(a+...己知cos(兀/4一a)=3/5,sin(5兀/4十b)=-12/13,a属于(兀/4,3兀/4),b属于(O,兀/4).求sin(a+b)的值
cos(π/4一a) = cos(a-π/4) = 3/5 ==> sin(a-π/4) = 4/5
sin(5π/4+b) = -sin(π/4+b) ==> sin(b+π/4) = 12/13;cos(b+π/4) =5/13
sin(a+b)=sin[(a-π/4)+(b+π/4)] = 56/65 /*两角和公式
由题设可得
cos(a-π/4)=3/5
sin(a-π/4)=4/5
sin(b+π/4)=12/13
cos(b+π/4)=5/13
sin(a+b)
=sin[(a-π/4)+(b+π/4)]
=(4/5)(5/13)+(3/5)(12/13)
=56/65
我也不会