几道数学题:若x+2y=3,xy=2,则x2+4y2=______..已知(x+y)2=9,(x-y)2=5,则xy=
问题描述:
几道数学题:若x+2y=3,xy=2,则x2+4y2=______..已知(x+y)2=9,(x-y)2=5,则xy=
答
x²+4y²=(x+2y)²-4xy=3²-4×2=1
4xy=(x+y)²-(x-y)²=9-5=4
xy=1