Question
The number of common tangents to the circles $x^{2}+y^{2}-4 x-6 x-12$ $=0$ and $x^{2}+y^{2}+6 x+18 y+26=0$, is: (a) 3(b) 4(c) 1(d) 2
Step 1
The general equation of a circle is $x^{2}+y^{2}+2gx+2fy+c=0$, where the center is $(-g,-f)$ and the radius is $\sqrt{g^{2}+f^{2}-c}$. For the first circle, $x^{2}+y^{2}-4x-6y-12=0$, the center $C_1$ is $(2,3)$ and the radius $R_1$ is Show more…
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