Ex3.若锐角a,b满足tana•tanb=13/7,且sin(a-b)=3分之根号下5 求cos(a+b)=?
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![Ex3.若锐角a,b满足tana•tanb=13/7,且sin(a-b)=3分之根号下5 求cos(a+b)=?](/uploads/image/z/2650590-54-0.jpg?t=Ex3.%E8%8B%A5%E9%94%90%E8%A7%92a%2Cb%E6%BB%A1%E8%B6%B3tana%26%238226%3Btanb%3D13%2F7%2C%E4%B8%94sin%28a-b%29%3D3%E5%88%86%E4%B9%8B%E6%A0%B9%E5%8F%B7%E4%B8%8B5+%E6%B1%82cos%28a%2Bb%29%3D%3F)
Ex3.若锐角a,b满足tana•tanb=13/7,且sin(a-b)=3分之根号下5 求cos(a+b)=?
Ex3.若锐角a,b满足tana•tanb=13/7,且sin(a-b)=3分之根号下5 求cos(a+b)=?
Ex3.若锐角a,b满足tana•tanb=13/7,且sin(a-b)=3分之根号下5 求cos(a+b)=?
锐角a,b
cos(a-b)=2/3
cosa*cosb-sina*sinb=2/3
tana•tanb=13/7
sina*sinb/cosa*cosb=13/7
cos(a+b)=cosa*cosb+sina*sinb
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