x-2y的最大值是 10 .将方程x^2+y^2-2x+4y=0化为圆的标准形式,得(x-1)^2 + (y+2)^2 = 5令x-1 = √5sinty+2 = √5cost则x-2y = √5sint - 2√5cost + 5= √5(sint -2cost) + 5= √5*√5(√5/5sint - 2√5/5cost) + 5= ...