第59页 - 苏科版七年级伴你学数学答案（上下册）

C

$解：原式=-{(x+y)}^{2}$

$解：原式=3a({x}^{2}+2xy+{y}^{2})$

$=3a{(x+y)}^{2}$

$解：原式=\frac 1 3({x}^{2}-9{y}^{2})$

$=\frac 1 3(x+3y)(x-3y)$

$解：原式=({x}^{2}+9)({x}^{2}-9)$

$=({x}^{2}+9)(x+3)(x-3)$

$解：原式={x}^{4}+{y}^{4}+2{x}^{2}{y}^{2}-4{x}^{2}{y}^{2}$

$={x}^{4}+{y}^{4}-2{x}^{2}{y}^{2}$

$={({x}^{2}-{y}^{2})}^{2}$

$={(x-y)}^{2}{(x+y)}^{2}$

$解：原式=({x}^{2}-2y+1-2y)({x}^{2}-2y-1+2y)$

$=({x}^{2}-4y+1)({x}^{2}-1)$

$=({x}^{2}-4y+1)(x+1)(x-1)$

$解：{x}^{4}+{x}^{2}+1={x}^{4}+2{x}^{2}+1-{x}^{2}={({x}^{2}+1)}^{2}-{x}^{2}=({x}^{2}+1+x)({x}^{2}+1-x)$

解：由图可知，$3{a}^2+4ab+{b}^2=(3a+b)(a+b)$