首先你知道tan (x/2)=(sinx)/(cosx+1)吗?
接下来
f(x1+x2)/2=sin(x1+x2)/[cos(x1+x2)+1]
(fx1+fx1)/2=1/2(sinx1/cosx1+sinx2/cosx2)
=1/2((sinx1cosx2+sinx2cosx1)/cosx1cosx2)) (直接通分)
=1/2(sin(x1+x2))/cosx1cosx2)
所以即证
2cosx1cosx2
首先你知道tan (x/2)=(sinx)/(cosx+1)吗?
接下来
f(x1+x2)/2=sin(x1+x2)/[cos(x1+x2)+1]
(fx1+fx1)/2=1/2(sinx1/cosx1+sinx2/cosx2)
=1/2((sinx1cosx2+sinx2cosx1)/cosx1cosx2)) (直接通分)
=1/2(sin(x1+x2))/cosx1cosx2)
所以即证
2cosx1cosx2