Find the twice of the cofficient of a2b2 in (4a2 + 9b2)2

72 36 144 288

144

(4a2 + 9b2)2 = 16a4 + 81b4 + 2×4a2×9b2 = 16a4 + 81b4 + 72a2b2 Here the coefficient of a2b2 = 72 So, 72×2 = 144