Question

If 1^2 +2^2 +3^2 +..........+ 10^2 = 385 , find 1/2 × ( 2^2 + 4^2 + 6^2 +.........+ 20^2)

Answer 1

$\frac{1}{2} \times 4( {1}^{2} + {2}^{2} + {3}^{2} + .... + {10}^{2} )$

$= 2(385)$

$= 770$