1)(2x+5.2)/3=4.1/1.5 |*3
2x+5.2=8.2
2x=8.2-5.2
2x=3
x=1.5
2)1.8/(x+1)=0.9/2.5
прекрёстно умножить
1.8*2.5=(x+1)*0.9
4.5=0.9x+0.9
0.9x=4.5-0.9
0.9x=3.6
x=3.6/0.9
x=4
3)8/12.8=(x-3)/3.2 |*12.8
8=4x-12
4x=12+8
4x=20
x=5
4)(3x-2.2)/8=3.4/4 |*8
3x-2.2=6.8
3x=6.8+2.2
3x=9
x=9/3
x=3