（x+y)²-（x-y)(3y-x)其中x=5/2,y=-1/2
=x²+2xy+y²-3xy+3y²+x²-xy
=2x²-2xy+4y²
=2(x²-xy+2y²)
=2(25/4+5/4+1)
=17
（b-a)²+b(a-b) 其中a=5,b=-1/5
=(a-b)(a-b+b)
=a(a-b)
=5(5+1/5)
=25+1
=26