The circle C C\,C has equation x2+y2+8x−4y+k=0x^2 + y^2 + 8x - 4y + k = 0x2+y2+8x−4y+k=0 where k k\,k is a constant.
C C\,C passes through the point (1,5)(1, 5)(1,5).
Find the value of kkk.
Rewrite the equation of C C\,C in centre-radius form, then state its centre and exact radius.
8 exam-style questions on OCR A Level Maths 1.3.4 Coordinate geometry of a circle. Each one has a worked solution and a mark scheme showing where the marks go.