A50:a20 =-1
(a1+49d):(a1+19d) =-1
a1+49d =-a1-19d
2a1 =-68d
a1=-34d
an=a1+(n-1)•d=0
-68d+nd-d=0
-69d+nd=0
nd=69d
n=69
116:4=29
29×29=841
Ответ S = 841 см2
1/2×5=5/10
1/4×25=25/100
1/8×125=125/1000
1/5×2=2/10
1/25×4=4/100
1/125×8=8/1000
3/4×25=75/100
4/5×2=8/10
12x:(x+2)=18
12x:x+12x:2=18
12+6x=18
6x=6
X=6