cos[arctan(1/2) - arctan(-2)]=?

cos[arctan(1/2) - arctan(-2)]=? cos[2arctan(-1/2)]=? 计算cos(1/2arctan(-3/4)) cos[1/2arctan(-3/4)].cos[1/2arctan(-3/4)]= cos(arctan(-2)-arcsin3/5) 求值1.cos[arcsin(-4/5)-arctan(-3/4)]2.sin[1/2arcsin(-12/13)] 求值arctan（ cot2）,tan(1/2arccos4/5),cos[arcsin(-3/5)],arcsin(cos1/3) 高一数学：tan[arcsin1+arctan(-√3/3)]+cos[arccos(-1/2)+arctan0] 对函数y=ln[cos(arctan(sinx))]求导最后答案是-sinxcosx/(1+sinx^2) cos(2arctan√2+π/3)的值为 求值cos(2arctan根号6+pai/3) cos(2arctan根号6+三分之派）＝? 求 cos[2arctan(3/4)]的值 cos(arctan(-2)) = 能不能给讲解下谢谢 arctan(1/3)+arctan(1/2)的值为? 级数求和：arctan(1/2)+arctan(1/2^2)+arctan(1/2^3)+...+arctan(1/2^n)+... arctan(1/2)?是多少?谢谢 求证：arctan 1/2+arctan 1/5+arctan 1/8=π/4