104 x 109 = (100 + 4)(100 + 9)

Using identity -

(x + a)(x + b) = x² + (a + b)x + ab, we get –

Take 104 = 100 + 4 and 109 = 100 + 9

104 x 109 = 100² + (4 + 9)100 + 4× 9

= 10000 + 1300 + 36

= 11336