Đáp án:
Giải thích các bước giải:
Bài 22 :
a ) ( x - a ) ( x - b ) ( x + c ) = ( x² - bx - ax + ab ) ( x + c )
= x³ + cx² - bx² - bcx - ax² - acx + abx + abc
b) ( x + y ) ( x^4 - x³y + x²y² - xy³ + y^4 ) = x^5 - x^4y + x³y²-x²y³+xy^4 + x^4y - x³y²+ x²y³- xy^4 + y^5
= x^5 + y^5
c) ( a + 1 ) ( a^6 - a^5 + a ^4 - a³ + a² - a + 1 )
= a^7 - a^6 + a^5 - a^4 + a³-a² + a + a^6 - a^5 + a^4 - a³ + a² - 1
= a^7 + 1
bài 23 : Tìm x biết :
a) 4 ( x+5 ) ( 2x - 3 ) - 8 ( x - 1 ) ( x + 4 ) = 0
8x² - 12x + 40x - 60x - 8x² - 32x + 8x +32x = 0
4x - 28 = 0
x = 7
b ) ( 2x+7 ) ( 5x + 6 ) - ( x + 1) ( 10x + 17 ) = ( x + 2 ) - ( x - 7 )
10x² + 12x + 35x + 42 - ( 10x² + 17x + 10x + 17 ) = x+2-x+7
10x² + 12x + 35 x + 42 - ( 10x² + 27x + 17 ) = 9
10x² 12x + 35x + 42 - 10x² - 27x - 17 = 9
20x + 25x = 9
20x = 9 -25
20x = -16
x = -4/5
