Bài 3
a, 2x(x-1)-x(4-x)=0
⇒ 2x²-2x-4x+x² =0
⇒ 3x²-6x =0
⇒ 3x(x-2) =0
⇒3x=0 hoặc x-2=0
⇒ x=0 hoặc x =2
b, 0,25x²-(0,5x-4).0,5x=-14
⇒ 0,25x²-0,25x²+2x =-14
⇒2x=-14
⇒ x=-14:2
⇒ x=-7
Bài 4
a, $5^{n+1}$-2. $5^{n}$
=$5^{n}$.5-2.$5^{n}$
=$5^{n}$(5-2)
=$5^{n}$.3
b, $2x^{n-1}$( $x^{n+1}$- $y^{n+1}$)+ $y^{n+1}$( $2x^{n-1}$ - $y^{n-1}$ )
= $2x^{2(n-1)(n+1)}$-$2xy^{(n-1)(n+1)}$ +$2xy^{(n-1)(n+1)}$- $y^{2(n-1)(n+1)}$
= $2x^{2n^2-2}$- $y^{2n^2-2}$
= $(2x-y)^{2n^2-2}$
