作业帮一、(-5x+2y)(-2y+5x)二、[(-x-1/4y)^2+(x-1/4y)^2](2x^2-1/8y^2)三、化简求值；(-2x-3)(2x-3)+(3x-2)^2+(x+1)(x+3),其中X=-1四、已知a-b=3,ab=4,求a^2+b^2的值和a^2-b^2的值
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一、(-5x+2y)(-2y+5x)二、[(-x-1/4y)^2+(x-1/4y)^2](2x^2-1/8y^2)三、化简求值；(-2x-3)(2x-3)+(3x-2)^2+(x+1)(x+3),其中X=-1四、已知a-b=3,ab=4,求a^2+b^2的值和a^2-b^2的值
一、(-5x+2y)(-2y+5x)
二、[(-x-1/4y)^2+(x-1/4y)^2](2x^2-1/8y^2)
三、化简求值；(-2x-3)(2x-3)+(3x-2)^2+(x+1)(x+3),其中X=-1
四、已知a-b=3,ab=4,求a^2+b^2的值和a^2-b^2的值
一、(-5x+2y)(-2y+5x)二、[(-x-1/4y)^2+(x-1/4y)^2](2x^2-1/8y^2)三、化简求值；(-2x-3)(2x-3)+(3x-2)^2+(x+1)(x+3),其中X=-1四、已知a-b=3,ab=4,求a^2+b^2的值和a^2-b^2的值
1.
(-5x+2y)(-2y+5x)
=-(5x-2y)(5x-2y)
=-(5x-2y)^2
=-(25x^2-20xy+4y^2)
=20xy-25x^2-4y^2
2.
[(-x-1/4y)^2+(x-1/4y)^2](2x^2-1/8y^2)
=[(x+1/4y)^2+(x-1/4y)^2](2x^2-1/8y^2)
=(x^2+1/2y+1/16y^2+x^2-1/2y+1/16y^2)(2x^2-1/8y^2)
=(2x^2+1/8y^2)(2x^2-1/8y^2)
=4x^4-1/64y^4
3.
(-2x-3)(2x-3)+(3x-2)^2+(x+1)(x+3)
=(3+2x)(3-2x)+(3x-2)^2+(x+1)(x+3)
=9-4x^2+9x^2-6x+4+x^2+3x+x+3
=6x^2-2x+16
=2(x^2-x+8)
=2*(1+1+8)
=20
4.
a^2+b^2
=(a^2+b^2-2ab)+2ab
=(a-b)^2+2ab
=9+8
=17
(a+b)^2
=(a-b)^2+4ab
=9+16
=25
a+b=5或a+b=-5
a^2-b^2
=(a+b)(a-b)
=15或-15
1.-25x^2+20xy-4y^2
2.(2x^2+1/8y^2)(2x^2-1/8y62)=4x^4-1/64y^4
3.-4x^2+9+9x^2-12x+4+x^2+4x+3
=6x^2-8x+16
=6+8+16=30
4.a^2+b^2=(a-b)^2+2ab=9+8=17
∵(a+b)^2=(a-b)^2+4ab=9+16=25, a+b=±5
a^2-b^2=(a+b)(a-b)=±15