已知实数x y满足x-2y=3,则根号x2+y2最值是多少?

问题描述:

已知实数x y满足x-2y=3,则根号x2+y2最值是多少?

x-2y=3
x=2y+3
x²+y²
=(2y+3)²+y²
=5y²+12y+9
=5(y²+12y/5+36/25)+9/5
=5(x+6/5)²+9/5
最小值:y=9/5