Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2002/iii/paper-24/3/b/solution

Count affine solutions and then add the point at infinity. Over the finite field , both values of give , and both values of solve . Hence there are four affine points. Over , all three values of give zero, and each has the two ordinates , giving six affine points.
Over the finite field , completing the square gives . The square residues are . For , the right sides and the corresponding numbers of ordinates are
Their sum is sixteen. The resulting elliptic-curve point counts over a finite field are

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