S=π•R^2 (π=3,14)
1)S=3,14*2*2=3,14*4=23,56
2)S=3,14*5*5=3,14*25=78,5
3)S=99=3,14*R^2
R^2=9:3,14=2,86
R=√2,86=1.69
4)R=2/7
S=3.14*2/7*2/7=3,14*4/49=3,14*0,08= =0,25
5)S=49π=3,14*49
R=√49=7
6)R=54,3
S=3,14*54,3*54,3=3,14*2948,49= =9258,2586
7)R=√3
S=3,14*√3*√3=3,14*3=9,42
8)s=6,25=3,14*R^2
R^2=6,25:3,14=1,99
R=√1,99=1,4