9)BAD=1/2*BAC=1/2*62=31
10)AB=2R=20*2=40
AC^2=AB^2-CB^2=1600-1024=576
AC=24
11)P=4a=84
a=84/4=21
S=21*21=441
12)
2,8×(57,6+42,4)=2,8×100=280
1) 30/100%=0,3*10%=3
2)12/100%=0,12*50%=6
3)15/100%=0,15*60%=9
4)20/100%=0,20*30%=6
S=a2 P=4a --> a=P/4 S=P^2/16 при 0.8P S=(0.64*P^2)/16 1-0,64=0,36 или 36%