设tan(α+8/7π)=a 求证sin(22π/7+α)+3cos(α-20π/7)/ sin(20π/7-α)-co
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设tan(α+8/7π)=a 求证sin(22π/7+α)+3cos(α-20π/7)/ sin(20π/7-α)-cos(α+22π/7)=a+3/-a
tan(α+8π/7)=tan(π+α+π/7)=tan(α+π/7),即:tan(α+π/7)=a
sin(22π/7+α)+3cos(α-20π/7)/ sin(20π/7-α)-cos(α+22π/7)
=(sin(3π+π/7+α)+3cos(3π-2π/7-α))/(sin(3π-2π/7-α)-cos(3π+π/7+α))
=-(sin(π/7+α)+3cos(2π/7+α))/(sin(2π/7+α)+cos(π/7+α))
=-(sin(π/7+α)+3(cosπ/7cos(π/7+α)-sinπ/7sin(π/7+α)))/(sinπ/7cos(π/7+α)+cosπ/7sin(π/7+α)+cos(π/7+α))
=-(tan(π/7+α)+3(cosπ/7-sinπ/7tan(π/7+α)))/(sinπ/7+cosπ/7tan(π/7+α)+1)
=-(a+3(cosπ/7-asinπ/7))/(sinπ/7+acosπ/7+1)
sin(22π/7+α)+3cos(α-20π/7)/ sin(20π/7-α)-cos(α+22π/7)
=(sin(3π+π/7+α)+3cos(3π-2π/7-α))/(sin(3π-2π/7-α)-cos(3π+π/7+α))
=-(sin(π/7+α)+3cos(2π/7+α))/(sin(2π/7+α)+cos(π/7+α))
=-(sin(π/7+α)+3(cosπ/7cos(π/7+α)-sinπ/7sin(π/7+α)))/(sinπ/7cos(π/7+α)+cosπ/7sin(π/7+α)+cos(π/7+α))
=-(tan(π/7+α)+3(cosπ/7-sinπ/7tan(π/7+α)))/(sinπ/7+cosπ/7tan(π/7+α)+1)
=-(a+3(cosπ/7-asinπ/7))/(sinπ/7+acosπ/7+1)
设tan(α+8/7π)=a 求证sin(22π/7+α)+3cos(α-20π/7)/ sin(20π/7-α)-co
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