Question

4+8+12+....+360= afla suma

Answer 1

$\displaystyle 4+8+12+...+360=4(1+2+3+...+90)=4 \times \frac{90(90+1)}{2} = \\ \\ =4 \times \frac{90 \times 91}{2} =4 \times \frac{8190}{2} =4 \times 4095=16380$