实数x .y满足x2+y2 - 4x+2y - 4=0.则2x-y的最大值是?

x2+y2 - 4x+2y - 4=0x2-4x+4+y2+2y+1=5+4(x-2)2+(y+1)2=9设x=3sint+2y=3cost-1则有2x-y=6sint+6-3cost+1=6sint-3cost+7因为 √(6^2+3^2)=3√5所以2x-y=3√5(6/3√5sint-3/3√5cost)+7令cosA=6/3√5所以sinA=√(1-cos...