(COSX-SINX)/(2-COSX)
=[(cost)^2-(sint)^2-2sintcost]/[3(sint)^2+(cost)^2 (t=x/2,输入不方便,手写可以直接写成x/2)
=[1-(tant)^2-2tant]/[3(tant)^2+1]
令tant=k,k属于R
上式=(1-k^2-2k)/(3k^2+1)=y
1-k^2-2k=3yk^2+y
(3y+1)k^2+2k+(y-1)=0
判别式=4-4(y-1)(3y+1)≥0
(1-√7)/3≤y≤(1+√7)/3 (COSX-SINX)/(2-COSX)
=[(cost)^2-(sint)^2-2sintcost]/[3(sint)^2+(cost)^2 (t=x/2,输入不方便,手写可以直接写成x/2)
=[1-(tant)^2-2tant]/[3(tant)^2+1]
令tant=k,k属于R
上式=(1-k^2-2k)/(3k^2+1)=y
1-k^2-2k=3yk^2+y
(3y+1)k^2+2k+(y-1)=0
判别式=4-4(y-1)(3y+1)≥0
(1-√7)/3≤y≤(1+√7)/3