If two circles are such that the centre of one lies on the circumferen...
1:b) 2:c) $\sqrt{2}$:d) $\frac{1}{\sqrt{2}}$
Answer: $\boxed{\textbf{(c) }\sqrt{2}}$
Solution: Let $O_1$ and $O_2$ be the centers of circles with radii $r_1$ and $r_2,$ respectively, and let $AB$ be the common chord. Without loss of generality, assume that circle $O_1$ is inside circle $O_2.$
[asy] unitsize(0.8cm); pair O1 = (0,0), O2 = (2,0); real r1 = 1.5, r2 = 2.5; pair A = (-1.5*sqrt(2),-1.5), B = (1.5*sqrt(2),-1.5); draw(Circle(O1,r1)); draw(Circle(O2,r2)); draw(A--B); label("$O_1$",O1,NW); label("$O_2$",O2,NW); dot("$A$",A,SW); dot("$B$",B,SE); label("$r_1$",O1--O1+dir(-90)*r1,SW); label("$r_2$",O2--O2+dir(-90)*r2,SW); draw(O1--A--O2--cycle,dashed); [/asy]
Since $O_1A=r_1$ and $O_2B=r_2,$ we have \[AB = O_1A + O_2B = r_1+r_2.\] By the Pythagorean Theorem, we have \[O_1O_2 = \sqrt{(O_1A)^2 + (O_2B)^2} = \sqrt{r_1^2 + r_2^2}.\] Then by the Pythagorean Theorem on right triangle $O_1O_2B,$ \[O_1B = \sqrt{O_1O_2^2 - O_2B^2} = \sqrt{r_1^2 + r_2^2 - r_2^2} = \sqrt{r_1^2} = r_1.\] Thus, \[AB = r_1 + r_2 = \sqrt{2}\cdot r_1,\] and the desired ratio is $\boxed{\sqrt{2}}.$