1) -8х=72
х= 72:(-8)
х=-9
2) 0,9х=-5,4
х= -5,4:0,9= -54:9
х=-6
3) -1,7х=-5,1
х=(-5,1):(-1,7)= (-51):(-17)
х=3
Cos(180-30)/sin40-sin(180-30)/cos40=-cos30/sin40-sin30/cos40=
=-(cos30cos40+sin30sin40)/sin40cos40=-cos(40-30):1/2sin80=
<span>-cos10:1/2sin(90-10)=-cos10:1/2cos10=-2</span>