1+ctg²(π/5)=1/sin²(π/5)
2cos12*cos48=2*1/2(cos12-48)+cos(12+48))=cos36+cos60=cos36+1/2
sin40-sin18=2sin(40-18)/2*cos(40+18)/2=2sin22*cos29
Log5(7-2x)=3log5(2)
log5(7-2x)=log5(2^3)
log5(7-2x)=log5(8)
7-2x=8 2x=-1 x=-1/2
10х+9>-6-15х
10х+15х>-6-9
25х>-15
х>-0.6
5y(3y-2)-(y-1)(y+1)=15y²-10y-y²+1=14y²-10y+1
(b-8)(b+4)+(b-5)²=b²+4b-8b-32+b²-10b+25=2b²-14b-7
6(c+d)²-12cd=6(c²+2cd+d²)-12cd=6c²+12cd+6d²-12cd=6c²+6d²=6(c²+d²)