七年级数学题计算题

Question

1.(a^2+ab+b^2)(a^2-ab+b^2)
2.(7x-6y)^2+2(7x-6y)(7x+6y)+(7x+6y)^2
化简求值
1.(2x+y)(2x-y)+(x+y)^2-2(2x^2-xy)其中x=1,y=-1/4
2.已知x=6.61,y=-3.39.求(x-y)(x^2+3xy+y^2)-5xy*(x-y)的值

Answer 1

1.(a^2+ab+b^2)(a^2-ab+b^2)
=[(a^2+b^2)+ab][(a^2+b^2)-ab]
=(a^2+b^2)^2-a^2b^2
=a^4+2a^2b^2+b^4-a^2b^2
=a^4+a^2b^2+b^4

2.(7x-6y)^2+2(7x-6y)(7x+6y)+(7x+6y)^2
=(7x-6y+7x+6y)^2
=(14x)^2
=196x^2

1.(2x+y)(2x-y)+(x+y)^2-2(2x^2-xy)其中x=1,y=-1/4
=4x^2-y^2+x^2+2xy+y^2-4x^2+2xy
=x^2+4xy
=x(x+4y)
=1*(1-1)
=0

2.已知x=6.61,y=-3.39.
(x-y)(x^2+3xy+y^2)-5xy*(x-y)
=(x-y)(x^2+3xy+y^2-5xy)
=(x-y)(x^2-2xy+y^2)
=(x-y)(x-y)^2
=(x-y)^3
=(6.61+3.39)^3
=10^3
=1000

Answer 2

其实很简单的..
但是化起来很麻烦