Question

Dùng hẳng đẳng thức để khai triển và thu gọn

a) (6x+5y) ( 6x-5y) 

b) (-4xy-5)(5-4xy)

c) (3x-4)^2 +2.(3x - 4 ) . ( 4-x ) + (4-x)^2

Answer 1

\(a,\left(6x+5y\right)\left(6x-5y\right)\)

\(=\left(6x\right)^2-\left(5y\right)^2\)

\(=36x^2-25x^2\)

\(b,\left(-4xy-5\right)\left(5-4xy\right)\)

\(=-\left(5+4xy\right)\left(5-4xy\right)\)

\(=-[5^2-\left(4xy\right)^2]\)

\(=-\left(25-16xy^2\right)\)

\(c,\left(3x-4\right)^2+2.\left(3x-4\right).\left(4-x\right)+\left(4-x\right)^2\)

\(=\left(3x-4\right)\left(3x-4+2\right)\left(4-x\right)\left(1+4-x\right)\)

\(=\left(3x-4\right)\left(3x-2\right)\left(4-x\right)\left(5-x\right)\)