1.(1)4xy-3x²-xy+y²+x²-3xy-2y+2x²
=(4xy-xy-3xy)+(-3x²+x²+2x²)+y²-2y
=0+0+y²-2y
=y²-2y
将x=1又13/15,y=-1代入上式得:
y²-2y =1²-2x1=-1
(2)5a²-[a²+(5a²-2a)-2(a²-3a)]
=5a²-(a²+5a²-2a-2a²+6a)
=5a²-【(a²+5a²-2a²)+(-2a+6a)】
=5a²-(4a²+4a)
=5a²-4a²-4a
=a²-4a
=a(a-4)
将a=1/2代入上式得:
a(a-4)=1/2(1/2-4)=-1.75 (你要需要分数你就化成分数)
2(2)选择C
就会仨题啊 剩下的 好好想想吧