已知f(a)=tan(π-a)*cos(2π-a)*sin(π/2+a)/cos(-a-π).1.化简f(a) 2.若f(a)=4/5,a为第二象限角,求cos(2a+π/4)
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![已知f(a)=tan(π-a)*cos(2π-a)*sin(π/2+a)/cos(-a-π).1.化简f(a) 2.若f(a)=4/5,a为第二象限角,求cos(2a+π/4)](/uploads/image/z/6865883-35-3.jpg?t=%E5%B7%B2%E7%9F%A5f%28a%29%3Dtan%28%CF%80-a%29%2Acos%282%CF%80-a%29%2Asin%28%CF%80%2F2%2Ba%29%2Fcos%28-a-%CF%80%29.1.%E5%8C%96%E7%AE%80f%EF%BC%88a%EF%BC%89+2.%E8%8B%A5f%EF%BC%88a%EF%BC%89%3D4%2F5%2Ca%E4%B8%BA%E7%AC%AC%E4%BA%8C%E8%B1%A1%E9%99%90%E8%A7%92%2C%E6%B1%82cos%EF%BC%882a%2B%CF%80%2F4%EF%BC%89)
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已知f(a)=tan(π-a)*cos(2π-a)*sin(π/2+a)/cos(-a-π).1.化简f(a) 2.若f(a)=4/5,a为第二象限角,求cos(2a+π/4)
已知f(a)=tan(π-a)*cos(2π-a)*sin(π/2+a)/cos(-a-π).1.化简f(a) 2.若f(a)=4/5,a为第二象限角,求cos(2a+π/4)
已知f(a)=tan(π-a)*cos(2π-a)*sin(π/2+a)/cos(-a-π).1.化简f(a) 2.若f(a)=4/5,a为第二象限角,求cos(2a+π/4)
f(a)=-tana*cos(-a)*cosa/cos(a+π)
=-tanacosacosa/(-cosa)
=sina/cosa*cosa
=sina
f(a)=sina=4/5
a为第二象限
∴cosa