Sin(П/12-П/4)=sin(П/12-3П/12)=sin(-П/6)=-1/2
1)cost/(1+cost)+cost/(1-sint)=((cost(1-sint+1+sint))/(1+sint)*(1-sint)=2cost/cos^2t=2/cost
2)tqx+1/(1-ctqx)=1/ctqx+1/(1-ctqx)=(1-ctqx+ctqx)/(ctqx(-ctqx)=1/(ctqx-ctq^2x)
25x^2=<0<br />x=<0<br />Ответ: (-~;0]