Question

5 zadań z ciągów.

Answer 1

zad.11

a₁=12

an=99

n=30

Sn=(a1+an)/2*n=((12+99)/2)*30=(111/2)*30=55,5*30=1665

 

zad.12

a1=12

an=97

n=18

 

Sn=[(12+97)/2]*18=(109/2)*18=981

 

zad.13

a1=24

a1+7n=56

7n=56-24=32

n=4 4/7

a2=28 4/7

a3=33 1/7

a4=37 5/7

a5=42 2/7

a6= 46 6/7

a7= 51 3/7

a8= 56

 

zad.14

a1=142

a1+5n=106

106-142=5n

5n=-36

n=-7 1/5

 

a2=134 4/5

a3= 127 3/5

a4= 120 2/5

a5= 113 1/5

a6= 106

 

zad.15

a+a+n+a+2n=120

3a+3n=120

a=20

b=40

c=60

P=20*40/2=800/2=400