x^2+(y-1)^2=9,
令
x=3cost
y-1=3sint y=3sint+1
x+y=3cost+3sint+1
=3√2(cost*√2/2+sint*√2/2)+1
=3√2cos(t-45°)+1
所以当cos(t-45°)=1时有最大值3√2+1令x=3costy-1=3sinty=3sint+1为什么啊因为当x=3costy-1=3sint有如下式x^2+(y-1)^2=(3cost)^2+(3sint)^2=9cos^2t+9sin^2t=9(sin^2t+cos^2t)=9 即圆的方程了