電子課本網(wǎng) › 第80頁

第80頁

信息發(fā)布者：

14

6

b＜c＜a

$ \begin{aligned}解：原式&=4x2-4xy+y2-x2+y2 \\ &=3x2-4xy+2y2 \\ \end{aligned}$

$ \begin{aligned}解：原式&=[(3x+y)(3x-y)]2 \\ &=(9x2-y2)2 \\ &=81x?-18x2y2+y? \\ \end{aligned}$

$ \begin{aligned}解：原式&=[(x+2y)+3z][(x+2y)-3z] \\ &=(x+2y)2-9z2 \\ &=x2+4xy+4y2-9x2 \\ \end{aligned}$

$ \begin{aligned}解：原式&=y+y2-y-4y+4 \\ &=y2+y-y-4y+4 \\ &=y2-4y+4 \\ &=(y-2)2 \\ \end{aligned}$

$ \begin{aligned}解：原式&=(x-y)(9-m2) \\ &=(x-y)(3+m)(3-m) \\ \end{aligned}$

$ \begin{aligned}解：原式&=(x2+4y2+4xy)(x2+4y2-4xy) \\ &=(x+2y)2(x-2y)2 \\ \end{aligned}$

$ \begin{aligned}解：原式&=(y2-1)2-6(y2-1)+9 \\ &=[(y2-1)-3]2 \\ &=(y2-4)2 \\ &=[(y+2)(y-2)]2 \\ &=(y+2)2(y-2)2 \\ \end{aligned}$

$ \begin{aligned}解：原式&=9x2-4y2-4xy+4y2 \\ &=9x2-4xy \\ \end{aligned}$

$當(dāng)x=\frac{1}{3}，y=-2時$

$原式= 9×(\frac{1}{3})2-4×\frac{1}{3}×(-2)=\frac{11}{3}$

$ \begin{aligned}解：原式&=x2-6x+9+2x2+14x-4x-28-x2+4 \\ &=2x2+4x-15 \\ \end{aligned}$

$因為x2+2x-4=0，所以x2+2x=4$

$當(dāng)x2+2x=4時$

$原式=2(x2+2x)-15=2×4-15=-7.$

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