a) ( 5x³ - x +2 ) ( x-1 )
= 5x⁴ -5x³ - x² + 1 + 2x - 2
= 5x⁴ -5x³ - x² 2x - 1
b) ( 4x + 4 )(3 - x² - x³ )
= 12x - 8x³ - 4x⁴ + 12 - 4x² - 4x³
= -4x⁴ - 12x³ -4x² + 12x + 12

1. The picture which she was looking at was very beautiful
2. You should write the address which I'll give you
3. The movie which they are talking about is very fantastic
4. The woman who you are listening to teaches me E
5. The scientists who are researching the causes of cancer are making progress
6. Do you know the woman who is coming toward us ?
7. The people who are waiting for the bus in the rain are getting wet

( x + y ) ( x² - xy + y² )
= ( x+ y ) ( x - y )²
= ( x² - y² ) ( x - y )
* [ ( -10 )² - 1² ] ( -10 -1 ) = 99 . ( -11 ) = - 1089
* [ ( -1 )² - 0² ) ( -1 - 0 ) = 1 . ( -1 ) = -1
* [ 2 - ( -1 )² ] ( 2 + 1 ) = 1 . 3 = 3

101² = ( 100 + 1 )²
= 100² + 2.100.1 + 1 ( HĐT số 1 )
= 10000 + 200 + 1
= 10201

1 .B . a² + b² + c² + 2ab + 2ac + 2bc
2. A. x² + x +1

B=x⁷ - 26x⁶ + 27x⁵ - 47x⁴ - 73x³ + 50x² + x - 24
= x⁷ - ( x + 1 ) x⁶ + ( x +2 )x⁵ - ( 2x - 3 )x⁴ - ( 3x - 2 ) x³ + 2x .x² + x - ( x - 1 )
= x⁷ - x⁷ - x⁶ + x⁶ + 2x⁵ - 2x⁵ + 3x⁴ - 3x⁴ + 2x³ + 2x³ + x - x - 1
= 4x³ -1
Thay x = 25
4x³ - 1
= 4. 25³ - 1
= 4. 15625 - 1
= 62500 -1 = 62499

b, (x^2+xy+y^2) (x-y)
= ( x+ y )² ( x- y )
= ( x² - y ² ) ( x +y )

d. ( x² - 2xy + y² ) ( x-y )
= ( x- y )² ( x- y )
= ( x - y )³

5ⁿ⁺¹ - 4.5ⁿ
= 5ⁿ . 5 - 4 . 5ⁿ
= 5ⁿ ( 5 - 4 )
= 5ⁿ . 1 = 5ⁿ