Question

Calculati sumele.
2+4+6+....+98+100
3+6+9+....+180
Multumesc!!!

Answer 1

2+4+6+...+100=2(1+2+3+...+50)
2(50*51/2)=50*51=2550

3+6+9+....+180=3(1+2+...+60)
3*(60*61/2)=3*30*61=5490

Answer 2

$\displaystyle a).2+4+6+...+98+100=2(1+2+3+...+49+50)= \\ \\ =2 \times \frac{50(50+1)}{2} =2 \times \frac{50 \times 51}{2} =\not 2 \times \frac{2550}{\not 2} =2550 \\ \\ b).3+6+9+...+180=3(1+2+3+...+60)=3 \times \frac{60(60+1)}{2} = \\ \\ =3 \times \frac{60 \times 61}{2} = 3 \times \frac{3660}{2} =3 \times 1830=5490$