Bài 3 : Hằng đẳng thức dạng ( A – B ) ( A + B ) = A^2 – B^2
a) -( 5 + 4y ) ( 5 – 4y )
b) ( 2x – 3 ) ( 2x + 3 )
c) (1/2 x – 2y ) ( 1/2 x + 2y )
Bài 3 : Hằng đẳng thức dạng ( A – B ) ( A + B ) = A^2 – B^2
a) -( 5 + 4y ) ( 5 – 4y )
b) ( 2x – 3 ) ( 2x + 3 )
c) (1/2 x – 2y ) ( 1/2 x + 2y )
`a,-(5+4y)(5-4y)=-[5²-(4y)^2]=-(25-16y^2)=-25+16y^2`
`b,(2x-3)(2x+3)=[(2x)^2-3^2]=4x^2-9`
`c,(1/2x-2y)(1/2x+2y)=[(1/2x)^2-(2y)^2]=1/4x^2-4y^2`
Đáp án:
\(\begin{array}{l} a,\ -(5+4y)(5-4y)=-25+16y^2\\ b,\ (2x-3)(2x+3)=4x^2-9\\ c,\ \bigg(\dfrac12x-2y\bigg)\bigg(\dfrac12x+2y\bigg)=\dfrac14x^2-4y^2\end{array}\)
Giải thích các bước giải:
\(\begin{array}{l} a,\ -(5+4y)(5-4y)\\ =-\left [5^2-(4y)^2\right ]\\ =-(25-16y^2)\\ =-25+16y^2\\ b,\ (2x-3)(2x+3)\\ =(2x)^2-3^2\\ =4x^2-9\\ c,\ \bigg(\dfrac12x-2y\bigg)\bigg(\dfrac12x+2y\bigg)\\ =\bigg(\dfrac12x\bigg)^2-(2y)^2\\ =\dfrac14x^2-4y^2\end{array}\)
chúc bạn học tốt!