lm nhanh giúp mik vs mn

Đáp án:

Bài `7`:

`a) 82^2 - 18^2`

` = (82 - 18)(82 + 18)`

` = 64 . 100`

`=  6400`

`b) 26^2 + 52 . 24 + 24^2`

` = 26^2 + 2 . 26 . 24 + 24^2`

` = (26 + 24)^2`

` = 50^2 = 2500`

`c) (93^3 + 78^3)/171 - 93 . 78`

` = ( (93 + 78)(93^2 - 93.  78 + 78^2))/171 - 93 . 78`

` = (171 . (93^2 - 93 . 78 + 78^2))/171 - 93 . 78`

` = 93^2 - 93 . 78 + 78^2 - 93 . 78`

` = 93^2 - 2 . 93 . 78 + 78^2`

` = (93 - 78)^2`

` = 15^2 = 225`

`d) (57^2 - 18^2)/(76,5^2 - 1,5^2)`

` = ( (57 + 18)(57 - 18))/((76,5-1,5)(76,5 + 1,5))`

` = ( 75 . 39)/(75 . 78)`

` = (75 . 39)/(75 . 2 . 39)`

` = 1/2`