Question

求解第11题，要过程

Answer 1

11、(a+b)(x+y)=4

ax+ay+bx+by=4

ax+by+ay+bx=4

5+ay+bx=4

ay+bx=4-5

ay+bx=-1

    原式

=a²xy+b²xy+abx²+aby²

=a²xy+aby²+b²xy+abx²

=ay(ax+by)+bx(by+ax)

=5ay+5bx

=5(ay+bx)

=5×(-1)

=-5

 

Answer 2

(a+b)(x+y)(ax+by) = 20
=a^2x^2+b^y^2+(a^2+b^2+2ab)xy+ab(x^2+y^2)
=(ax+by)^2-2abxy +(a^2+b^2+2ab)xy+ab(x^2+y^2)
=25+(a^2+b^2)xy+ab(x^2+y^2)
所以(a^2+b^2)xy+ab(x^2+y^2)=-5