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216.設已給一正2n边形,其边依次为a_1,a_2…,a_(2n)點P与a_i的距离是d_i,若 d_1d_(n+1)+d_2d_(n+2)+…+d_nd_(2n)=k=常數試求點P的軌跡。 217.求出由拋物線y=x~2与直線y=n~2(n是整數)所圍成的區域內整點的个數,整點就是各个坐标都是整數的點。 218.若1/a+1/b+1/c=1/(a+b+c),証明a,b,c三數中必有兩个同值而反号。
216. Let a positive 2n edge be given, the edges of which are a_1, a_2..., a_(2n) The distance between point P and a_i is d_i, if d_1d_(n+1)+d_2d_(n+2)+...+ D_nd_(2n)=k=Constant Find the trajectory of point P. 217. Find the number of whole points in the area enclosed by the parabola y=x~2 and the straight line y=n~2 (n is an integer). The whole point is the point where each coordinate is an integer. 218. If 1/a + 1/b + 1/c = 1/(a + b + c), prove that there must be two identical values in the three numbers a, b, c and the opposite sign.