Question

Find the sum of the series given below 1(1!)+2(2!)

Answer 1

Step-by-step explanation:

$1( ! 1) + 2( ! 2) \\ = 1 (1) + 2(2 \times 1) \\( \because \: ! 1 = 1 \: and \: ! 2 = 2 \times 1 = 2)\\ = 1 \times 1 + 2 \times 2 \\ = 1 + 4 \\ = 5$