Ctg² 210° + ctg² 120° + tg² 135° = ctg²(180 + 30) + ctg²(90 + 30) + tg²(90 + 45)=
= ctg²30 + tg²30 + ctg²45 = (√3)² + (1/√3)² + 1 = 3 + 1/3 + 1 = (4)1/3
А) 2(5-3x)=6-5x
10-6x-6+5x=0
-x+4=0
-x=-4
x=4
б) 2(1-x)-4(2x+8)=8x+28
2-2x-8x-32-8x-28=0
-18x-58=0
-18x=58
x= -58/18
в)1/2+1/4x=x-3/4
0,5+0,25x-x+0,75=0
-0,75x+1,25=0
-0,75x=-1,25
0,75x=1,25
x=1,25/0,75
x=5/3