Rút gọn :
a. ( 7x + 4 ) \(^2\)- ( 7x + 4 )( 7x - 4 )
b. ( x + 2y )\(^3\)- 6xy( x + 2y )
c. ( 3x + y )( 9x\(^2\) - 3xy + y\(^2\) ) - ( 3xy ) \(^3\) - 27x\(^2\)y
d. 5( x + 3 )( x - 3 ) + ( 2x + 3 )\(^2\) + ( x - 6 )\(^2\)
e. ( 2x + 3 )\(^2\) + ( 2x - 3 )\(^2\) - 2( 4x\(^2\) - 9 )
g. ( x + 2 )\(^3\) + ( x - 2 )\(^3\) + x\(^3\) - 3x( x + 2 )( x - 2 )
Mọi người giúp mình với . Mình đang cần gấp :33 .
a) (7x + 4)2 - (7x + 4)(7x - 4)
= 49x2 + 56x + 16 - 49x2 + 16
= 56x + 32
b) (x - 2y)3 - 6xy(x - 2y)
= x3 - 6x2y + 12xy2 - 8y3 - 6x2y + 12xy2
= x3 - 12x2y + 24xy2 - 8y3
c) (3x + y)(9x2 - 3xy + y2) - (3xy)3 - 27x2y
= 27x3 + y3 - (3xy)3 - 27x2y
d) 5(x + 3)(x - 3) + (2x + 3)2 + (x - 6)2
= 5x2 - 45 + 4x2 + 12x + 9 + x2 - 12x + 36
= 10x2
e) (2x + 3)2 + (2x - 3)2 - 2(4x2 - 9)
= (2x + 3)2 + (2x - 3)2 - 2(2x - 3)(2x + 3)
= (2x + 3 - 2x + 3)2
= 62 = 36
g) (x + 2)3 + (x - 2)3 + x3 - 3x(x - 2)(x + 2)
= (x+2+x-2)(x2 + 4x + 4 - x2 + 4 + x2 - 4x + 4) + x3 - 3x3 + 12x
= 2x(x2 + 8) + x3 - 3x3 + 12x
= 2x3 + 16x + x3 - 3x3 + 12x
= 28x
a, (7x + 4)2 - (7x + 4)(7x - 4)
= (7x + 4)(7x + 4 - 7x + 4)
= (7x + 4).8
= 56x + 32
b, (x + 2y)3 - 6xy(x + 2y)
= (x + 2y)[(x + 2y)2 - 6xy]
= (x + 2y)(x2 + 4xy + 4y2 - 6xy)
= (x + 2y)(x2 - 2xy + 4y2)
= x3 - 2x2y + 4xy2 + 2x2y - 4xy2 + 8y3
= x3 + 8y3
c, (3x + y)(9x2 - 3xy + y2) - (3xy)3 - 27x2y
= 27x3 + y3 - 27x3y3 - 27x2y
d, 5(x + 3)(x - 3) + (2x + 3)2 + (x - 6)2
= 5(x2 - 9) + 4x2 + 12x + 9 + x2 - 12x + 36
= 5x2 - 45 + 4x2 + 12x + 9 + x2 - 12x + 36
= 10x2
e, (2x + 3)2 + (2x - 3)2 - 2(4x2 - 9)
= 4x2 + 12x + 9 + 4x2 - 12x + 9 - 8x2 + 18
= 36
Chúc bn học tốt (Phần g mk giúp sau)
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