Question

那这个极限又是怎么等于的肋分母知道了..分子还是不清楚，脑子不行啊..

Answer 1

sinx=2sinx/2 *cosx/2 分母用这个定理就从左边推到右边了

分子sinx - sinπ/2 =sinx -1 = -(sinx/2 -cosx/2)²= (sinx/2 -cosx/2)(cosx/2 - sinx/2)=√2sin(x/2 -π/4)*√2cos(x/2+π/4)=2sin((x-π/2)/2)cos((x+π/2)/2)