Question

S= 7+14+21+...+693+700

Answer 1

S = 7 + 14 + 21 + ... + 693 + 700

S = 7 × ( 1 + 2 + 3 + ... + 100 )

S = 7 × ( 100 × 101 : 2 )

S = 7 × ( 10100 : 2 )

S = 7 × 5050

S = 35350

Answer 2

Răspuns:

a1=7

a2=14

a3=21

a2=(a1+a3)/2

14=28/2

14=14 A ⇒ progresie aritmetica, a2=a1+r⇒r=7

S=$\frac{(primul termen+ultimul termen)* numarul de termeni}{2}$

Numarul de termeni=n=100 termeni

an=700

an=a1+(n-1)*r

700=7+(n-1)*7

7+7n-7=700

7n=700

n=100

S=$\frac{(a1+a100)*100}{2}$

S=$\frac{(7+700)*100}{2}$

S=$\frac{707*100}{2}$

S=707*50

S=35350

Sper ca te-am ajutat! Am incercat sa fac pas cu pas. :)