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CAT Length of the Tangent - Practice Questions & MCQ

Edited By admin | Updated on Oct 04, 2023 04:20 PM | #CAT

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  • 5 Questions around this concept.

Solve by difficulty

The length of the tangent drawn from a point, whose distance from the center of a circle is 5 cm and the radius of the circle is 3 cm is:

The length of a tangent from a point (4, 4) to the circle x^2+y^2=4 is:

Concepts Covered - 1

Length of the Tangent

PT is a tangent to a circle and CT is radius of circle. Since, PT is perpendicular to CT. So, ΔPTC is a right angled triangle.

Using the pythagorean theorem

\\\mathrm{\;\;\;\;\;\;PC^2=PT^2+CT^2 } \\\Rightarrow \mathrm{\;PT^2=PC^2-CT^2}\\\text{Length of tangent is PT}\\\text{So,}\\\Rightarrow \;\;\mathrm{PT=\sqrt{PC^2-CT^2}}

Now, if we have given equation of circle \mathrm{ x^2+y^2=a^2} and coordinate of point P(x1, y1), then

\\\text {In } \Delta \mathrm{PTC}, \quad \mathrm{PT}^{2}=\mathrm{PC}^{2}-\mathrm{CT}^{2}\\ \text{Here for the circle} \mathrm{x^{2}+y^{2}=a^{2}}, \text{ coordinate of C is }(0,0)\\ \text { Hence, } \mathrm{PT}^{2}=(\sqrt{\left(\mathrm{x}_{1}-0\right)^{2}+\left(\mathrm{y}_{1}-0\right)^{2}}) ^{2}-(\sqrt{\mathrm{a}^{2}})^{2} \\ \Rightarrow \quad \mathrm{PT}=\sqrt{\mathrm{x}_{1}^{2}+\mathrm{y}_{1}^{2}-\mathrm{a}^{2}} \quad[\because \mathrm{CT}=\mathrm{radius}=\mathrm{a}]

If we have given general equation of circle \mathrm{ x^2+y^2+2gx+2fy+c=0} and coordinate of point P(x1, y1) from where tanget is drawn to the circle then, the length of tangent will be \sqrt{\mathrm{ x_1^2+y_1^2+2gx_1+2fy_1+c=0}}.

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