Kindly solve these 2 questions?

(a) If a circle is inscribed in a right angled triangle ABC with the right angle at B, show the diameter of the circle is equal to AB + BC – AC.

(b) If a triangle is inscribed in a circle, then the product of any two sides of the triangle is equal to the product of the diameter and the perpendicular distance of the third side from the opposite vertex. Prove the above statement.

1 Answer
Apr 6, 2017

(a)

drawn

O is the center of in-circle of the right angled triangle ABC in which /_ABC=90^@

O being the in-center of the DeltaABC

DeltaAODcongAOF

So AD=AF

OD=OF=r("radius of incircle")

DeltaCOEcongCOF

So CE=CF

OE=OF=r("radius")

DeltaBODcongBOE

So BD=BE

OD=OF=r("radius")

Again /_DBE=/_ABC=90^@

Hence BDOE" is a square"

Now

AB+BC-AC
=(BD+AD)+(BE+CE)-(AF+FC)

=(BD+BE)+AD-AF+CE-CF

=(r+r)+AD-AD+CE-CE

=2r="Diameter of the incircle"

(b)

drawn

By sine law we have for DeltaABC

a/sinA=b/sinB=c/sinC=2R.......[1],

where R is the radius of the circumcircle of DeltaABC

Now from relation [1] we have

b=2RsinB

=>bc=2RcsinB

=>bc=2Rcxxh/c,

where h is the length of the perpendicular from A to BC

So

=>bc=2Rxxh

="diameter" xx" length of the perpendicular from A to BC"

This relation can be proved similarly for any pair of sides of DeltaABC

So for a triangle inscribed in a circle, the product of any two sides of the triangle is equal to the product of the diameter and the perpendicular distance of the third side from the opposite vertex