Y RAJYALAKSHMI
Last Activity: 10 Years ago
12 + 16 + 24 + 40 …... = (8 + 4) + (8 + 4 * 2) + (8 + 4 * 2^2) + (8 + 4 * 2^3) + ….
= 8 + 8 + 8 + …. n terms + (4 + 4 * 2) + (4 * 2^2) + (4 * 2^3) + …. n terms
8 + 8 + 8 + …. n terms = 8n
(4 + 4 * 2) + (4 * 2^2) + (4 * 2^3) + …. n terms = 4(2^n – 1) /( 2 – 1) = 4(2^n – 1)
(This is in GP where a = 4 & 4 = 2, Sn = a( r^n – 1)/(r – 1)
Sun of the given series = 8n + 4(2^n – 1)