Đáp án:
$\\$
Ta xét vế trái : `(10x + 4)^2`
`= (10x + 4) (10x + 4)`
`= 10x (10x + 4) + 4 (10x + 4)`
`= 10x . 10x + 10x . 4 + 4 . 10x + 4 . 4`
`= 100x^2 + 40x + 40x + 16`
`= 100x^2 + [40x + 40x] + 16`
`= 100x^2 + [(40 + 40)x] + 16`
`= 100x^2 + 80x + 16` (Bằng với vế phải)
`-> (10x + 4)^2 = 100x^2 + 80x + 16`