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It is given that AB is …

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It is given that AB is a chord of a circle , with center O , such that AB =16 cm and radius of a circle is 10cm . tangents at A and B intersect each other at P . find the length of PA .
  • 1 answers

Sia ? 6 years, 4 months ago


We have, AB = 16 cm
{tex} \therefore{/tex} AL = BL = 8 cm [Perpendicular from the centre of the circle to a chord bisects it]
In {tex}\triangle{/tex}OLB, we have,
OB2 = OL2 + LB2
{tex} \Rightarrow{/tex} 102 = OL2 + 82
{tex} \Rightarrow{/tex} OL2 = 100 - 64 = 36
{tex} \Rightarrow{/tex} OL = 6 cm
Let PL = x and PB = y. Then, OP = (x + 6) cm.
Now, {tex} \angle PBO = 90^\circ{/tex}  as tangent makes a right angle with the radius of the circle at the point of contact.
In {tex}\triangle{/tex}'s PLB and OBP, we have,
PB2 = PL2 + BL2 and OP2 = OB2 + PB2
{tex} \Rightarrow{/tex} y2 = x2 + 64 and (x + 6)2 = 100 + y2 [Substituting the value of y2 in second equation]
{tex} \Rightarrow{/tex} (x + 6)2 = 100 + x2 + 64
{tex} \Rightarrow{/tex} 12x = 128
{tex}\Rightarrow x = \frac{{32}}{3}cm{/tex}
{tex} \therefore{/tex} y2 = x2 + 64
{tex} \Rightarrow {y^2} = {\left( {\frac{{32}}{3}} \right)^2} + 64 = \frac{{1600}}{9}{/tex}
{tex} \Rightarrow y = \frac{{40}}{3}cm{/tex}
Therefore, {tex} PA = PB = \frac{{40}}{3}cm{/tex}

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