X^2-10x-25-x^2+10x
-1/2=-0,5
-0,5*(-0,5)-10*(-0,5)-25-0,5*(-0,5)+10*(-0,5)=0,25+5-25+0,25-5=-25
Tc(5π/2-x)=ctgx=-√2
sin²x=1:(1+ctg²x)=1:(1+2)=1/3
sinx=1/√3
cosx=-√(1-sin²x)=-√(1-1/3)=-√6/3
cos(π/4+x)=cosπ/4cosx-sinπ/4sinx=
=√2/2*(-√6/3)-√2/2*√3/3=√2/2(-√6/3-√3/3)=-√6/6*(√2+1)
-2х=12
х=-6
3/7х=9
х=9/1×7/3
х=21
5х-15=0
5х=15
х=3
1/2х-1/3=1/6
1/2х=1/6+1/3
1/2х=1/6+2/6
1/2х=3/6=1/2
х=1/2×2/1
х=1
17.5х-0.5=34.5
17.5х=35
х=2
Cos105° +cos105°=2cos105° ~ -0.48