(sin x*sin 3x)sin^2 x+（cos x*cos 3x)cos^2 x 如何变到1/2[(cos 2x-cos4x)sin^2x+(cos2x+cos4x)cos^2x]

傅里叶级数作图f（x）=2sin[x] - sin[2x] + 2/3sin[3x] - 1/2sin[4x]我用mathematica输入程序Plot[{2sin[x],-2sin[x],2sin[x] - sin[2x],-2sin[x] + sin[2x],2sin[x] - sin[2x] + 2/3sin[3x],-2sin[x] + sin[2x] - 2/3sin[3x],2sin[x] - sin[2x] + 2/3si sin(x^2)/sin^2x 求导 (1-(sin^4x-sin^2xcos^2x+cos^4x)/sin^2x +3sin^2x 化简[1-(sin^4 x-sin^2 xcos^2 x+cos^4 x)]/(sin^2 x)+3sin^2 x sin x sin^2(π/3-x)+sin^2(π/6+x) -sin(3x/2)*sin(x/2)等于什么为什么 求不定积分【sin(x)^5 + sin(x)^3】^(1/2) 化简[1-(sin^4x-sin^2cos^2x+cos^4x)/(sin^2)]+3sin^2x 化简 sin²x+sin²(x+2π/3)+sin²(x-2π/3) 化简sin(-2x) lim(x(sin)^2) sin^2(x)求导 sin(2x)积分 s = 2*sin(x)-sin(2*x)+2/3*sin(3*x)-1/2*sin(4*x)+2/5*sin(5*x)用matlab画图,求教啊 sin(sin(x))的奇偶性 3sin^2x+-2sin^2y=2sinx sin^2x+-sin^2y=? 已知sin(x)+3cos(x)=2,求sin(x)-cos(x)/sin(x)+cos(x)=?