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10-1.Circle and System of Circles
normal
A circle passes through the points $(- 1, 1) , (0, 6)$ and $(5, 5)$ . The point$(s)$ on this circle, the tangent$(s)$ at which is/are parallel to the straight line joining the origin to its centre is/are :
A
$(1, - 5)$
B
$(5, 1)$
C
$(- 1, 5)$
D
$(B)$ or $(C)$ both
Solution
Note that $\Delta$ is right angled at $(0, 6)$ . Centre of the circle is $(2, 3)$ . Slope of the line joining origin to the centre is $3/2$. Take parametric equation of a line through $(2, 3)$ with $tan \theta = – \frac{2}{3}$ as $\frac{{x\,\, – \,\,2}}{{\cos \,\theta }} = \frac{{y\,\, – \,\,3}}{{\sin \,\theta }} = \pm \,r $ where $r = \sqrt{13}$.
Get the co-ordinates on the circle
Standard 11
Mathematics