4 - х + 2х - 6 = -13
х = -13 - 4 + 6
х = -11
Sin²a/(1+cosa)=(1-cos²a)/(1+cosa)=(1-cosa)(1+cosa)/(1+cosa)=1-cosa
1. 5 1/5:1 1/5=26/5:6/5=
26/5*5/6=26/6
2. 21/26*26/6=21/6
3. 5-21/6=(30-21)/6=9/6=
3/2
4. 30:3/2=30*2/3=10*2=20
1. 42:6=7
2.90-7=83
вроде так
48/19=2 10/19
427/16=26 11/16
221/17=13