Đáp án:
5a,
`A=x^2+4x+4-y^2`
`=(x+2)^2-y^2`
`=(x-y+2)(x+y+2)`
b,
Thay `x=106` và `y=8` vào `A` ta có:
`A=(106-8+2)(106+8+2)`
`=100·116`
`=11600`
6a,
`B=5x(x+1)-x-1`
`=5x(x+1)-(x+1)`
`=(x+1)(5x-1)`
b,
`B=0`
`<=>(x+1)(5x-1)=0`
`<=>`\(\left[\begin{array}{l}x+1=0\\5x-1=0\end{array}\right.\)`<=>`\(\left[\begin{array}{l}x=-1\\x=\dfrac{1}{5}\end{array}\right.\)
