Question

求数学学霸解答6.7.8.9.10题，求过程！谢谢！急需！

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Answer 1

Answer 2

6.已知a-b=3,ab=2
(1)(a+b)^2=a^2+2ab+b^2=a^2-2ab+b^2+4ab=(a-b)^2+4ab=3^2+4×2=17
(2)a^2-6ab+b^2=(a-b)^2-4ab=3^2-4×2=1
7.已知x+y=5.xy=1
(1)x^2+y^2=(x+y)^2-2xy=5^2-2×1=23
(2)(x-y)^2=x^2-2xy+y^2=x^2+2xy+y^2-4xy=(x+y)^2-4xy=5^2-4×1=21
8.已知(x+y)^2=4,(x-y)^2=3
(1)(x+y)^2=4,即x^2+2xy+y^2=4……① (x-y)^2=3,即x^2-2xy+y^2=3……②
①+②得2x^2+2y^2=7,即x^2+y^2=7/2
(2)①-②得4xy=1，即xy=1/4
9.已知x=-2
原式(x+1)(2x-1)-(x-3)^2=2x^2-x+2x-1-(x^2-6x+9)=x^2+7x-10=4-14-10=-20
10.已知a=√2-1
原式=（a+2)(a-2)+4(a+1)-4a=a^2-2a+2a-4+4a+4-4a=a^2=(√2-1)^2=3-2√2

Answer 3

6.（a-b）2=a2+b2-2ab=9 ab=2 a2+b2=13
(a+b)2=a2+b2+2ab
7.x2+y2=(x+y)2-2xy (x-y)2=x2+y2-2xy
8.(x+y)2=x2+y2+2xy =4 (x-y)2=x2+y2-2xy=3 两式相减 xy=1/4
9.=2x2-x+2x-1-x2+6x-9=x2+7x-10 带入x=-2
10.=a2-4+4a+4-4a=a2 带入a