In the given figure, PQ is a chord of length 8 cm of a circle of radius 5 cm. The tangents at P and Q intersect at a point T. Find the length TP.
Join OP and OT
Let OT intersect PQ at a point R.
Then, TP=TQ and ∠PTR=∠QTR.
∴TR⊥PQ
and TR bisects PQ.
∴PR=RQ=4 cm.
Also OR=√OP2−PR2=√52−42 cm
=√25−16 cm=√9 cm=3cm.
Let TP=x cm
and TR=y cm
From right ΔTRP, we get
TP2=TR2+PR2
⇒x2=y2+16
⇒x2−y2=16……(i)
From right ΔOPT, we get
TP2+OP2=OT2
⇒x2+52=(y+3)2 [OT2=(OR+RT)2]
⇒x2−y2=6y−16……(ii)
From (i) and (ii) , we get
6y−16=16⇒6y=32⇒y=163
Putting y=163 in (i) we get
x2=16+(163)2=(2569+16)=4009
⇒x=√4009=203
Hence , lenght TP=x cm=6.67 cm