题目

圆x2+y2=1内接等腰梯形ABCD,其中AB为圆的直径.设C(x,y)(x>0),记梯形ABCD的周长为f(x),求f(x)的解析式及最大值. 答案：解:过点C作CE⊥AB于E, 则OE=x(0<x<1), ∴EB=1-x. ∵x2+y2=1, ∴CB= =, ∴f(x)=2+2x+2(0<x<1), 令=t, 则2x=2-t2(0<t<). ∴f(x)=4-t2+2t=-(t-1)2+5≤5, 当t=1,即x=时f(x)有最大值为5.In order to develop the city, the government tries to beautify it as soon as possible. Several new special projects are ______.A．under constructB．under buildingC．under way D．under repair