Question

4+8+12.....+288
3+6+9+.....+162

Answer 1

$\displaystyle a).4+8+12+...+288=4(1+2+3+...+72)=4 \times \frac{72(72+1)}{2} = \\ \\ =4 \times \frac{72 \times 73}{2} =4 \times \frac{5256}{2} =4 \times 2628=10512 \\ \\ b).3+6+9+...+162=3(1+2+3+...+54)=3 \times \frac{54(54+1)}{2} = \\ \\ =3 \times \frac{54 \times 55}{2} =3 \times \frac{2970}{2} =3 \times 1485=4455$