Question

Scoate factor ul comun : 15+30+45+60+...... +600

Answer 1

15+30+45+60+...... +600

15(1+2+3+......40)

1+2+3+4+...+40=[40×(40+1)]:2=[40×41]:2=820

S=15×820=12300

sau variant a II a:

progresie aritmetica cu r=15

an=600, a1=15

an=a1+(n-1)×r

600=15+(n-1)×15

600=15+15n-15

n=600:15

n=40

S=[(a1+an)×n}:2=[(600+15)×40]:2

S=615×20

S=12300

15+30+45+60+...... +600 =12300

Answer 2

15+30+45+60+...+600=12300
dam factor comun pe 15 si obt
15(1+2+3+4+...+40)=15*820=12300
calculam suma lui Gauss pentru
1+2+3+4+...+40=[40*(40+1)]:2=[40*41]:2=820
sper ca te-am ajutat