高数题,

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高数题,
 

ds=√(1+(dx/dy)^2)dy
=√(1+(1/4)(y-1/y)^2)dy
=√(1+(1/4)(y^2+1/y^2-2))dy
=√((1/4)(y^2+1/y^2+2))dy
=(1/2)√(y+1/y)^2dy
=(1/2)(y+1/y)dy
则:s=∫[1-->e] (1/2)(y+1/y) dy
=(1/4)*y^2+(1/2)*lny | [1-->e]
=(1/4)(e^2-1)+1/2