The sketch shows circle C C\,C with centre P(6.5,7)P(6.5, 7)P(6.5,7). The line l l\,l with equation y=12x\displaystyle y = \frac{1}{2}xy=21x is a tangent to C C\,C at point Q(8,4)Q(8, 4)Q(8,4).

Find an equation for CCC.
The line with equation y=12x+k\displaystyle y = \frac{1}{2}x + ky=21x+k, where k k\,k is a non-zero constant, is also a tangent to CCC. Find the value of kkk.
67 exam-style questions on CCEA A Level Maths 1.2 Co-ordinate geometry in the x, y plane, covering 1.2.1 Co-ordinate geometry in the x, y plane, 1.2.2 Co-ordinate geometry in the x, y plane, 1.2.3 Co-ordinate geometry in the x, y plane, 1.2.4 Co-ordinate geometry in the x, y plane, 1.2.5 Co-ordinate geometry in the x, y plane, 1.2.6 Co-ordinate geometry in the x, y plane, 1.2.7 Co-ordinate geometry in the x, y plane, and 1.2 Co-ordinate geometry in the x, y plane. Each one has a worked solution and a mark scheme showing where the marks go.