①2(x+3)(x-3)=x²+(x-1)(x+1)+2x②5X+6(3X+2)(3X-2)=54(X-1/3)(X+1/3)+2③已知a-b=3,ab=1.求（a+b）²的值④x+y=3,xy=-2,求x²+y²的值

①2(x+3)(x-3)=x²+(x-1)(x+1)+2x②5X+6(3X+2)(3X-2)=54(X-1/3)(X+1/3)+2③已知a-b=3,ab=1.求（a+b）²的值④x+y=3,xy=-2,求x²+y²的值
①2(x+3)(x-3)=x²+(x-1)(x+1)+2x
②5X+6(3X+2)(3X-2)=54(X-1/3)(X+1/3)+2
③已知a-b=3,ab=1.求（a+b）²的值
④x+y=3,xy=-2,求x²+y²的值

①2(x+3)(x-3)=x²+(x-1)(x+1)+2x②5X+6(3X+2)(3X-2)=54(X-1/3)(X+1/3)+2③已知a-b=3,ab=1.求（a+b）²的值④x+y=3,xy=-2,求x²+y²的值
解
2(x+3)(x-3)=x²+(x-1)(x+1)+2x
2(x²-9)=x²+x²-1+2x
2x²-18=2x²-1+2x
即2x=-17
x=-17/2
5x+6(3x+2)(3x-2)=54(x-1/3)(x+1/3)+2
5x+6(9x²-4)=54(x²-1/9)+2
5x+54x²-24=54x²-6+2
5x=20
x=4
a-b=3,ab=1
(a+b)²
=(a-b)²+4ab
=3²+4×1
=13
x+y=3,xy=-2
x²+y²
=(x+y)²-2xy
=3²-2×(-2)
=13

1. ﹣8.5

2. 4

3. 13

4. 7

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