The circle C1 C_1\,C1 has equation x2+y2−4x+6y−12=0x^2+y^2-4x+6y-12=0x2+y2−4x+6y−12=0.
The circle C2 C_2\,C2 has equation (x−8)2+(y+3)2=k2(x-8)^2+(y+3)^2=k^2(x−8)2+(y+3)2=k2, where k>0k>0k>0.
Find all values of k k\,k for which the circles touch.
8 exam-style questions on WJEC A Level Maths 1.3.4 Coordinate geometry in the (x, y) plane. Each one has a worked solution and a mark scheme showing where the marks go.