Question

若集合M={（x,y）|y=x2},N={(x,y)|y=2x}则MN的并集的元素有多少个

Answer 1

y=x2

y=2x

x^2=2x

x^2-2x=0

x(x-2)=0

x1=0,y1=0

x2=2,y2=4

则MN的并集的元素有:{(x,y)|x=0,y=0;x=2,y=4}