In a triangle ABC, Let C=2π, If r is the inradius and R is circumradius of the triangle ABC, then 2(r+R) equals
Explanation
Concept:
Sine law:
sinAa=sinBb=sinCc=2R,
where a,b,c are sides and R is circumradius.
Inradius:
r=(s−a)tan(2A)=(s−b)tan(2B)=(s−c)tan(2C)
where a,b,c are sides, r is inradius, and s is semiperimeter
s=2a+b+c
Calculation:
Here, in triangle ABC, Let C=2π,
sinCc=2R
⇒2R=sin(π/2)c=c
R=2C
Now, inradius r=(s−c)tan(2C)
=(s−c)tan(4π)
=(s−c)
So, 2(r+R)=2(s−c+2C)=2(s−2C)
=a+b+c−c
=a+b
Hence, option (1) is correct.
Explanation
Concept:
Sine law:
sinAa=sinBb=sinCc=2R,
where a,b,c are sides and R is circumradius.
Inradius:
r=(s−a)tan(2A)=(s−b)tan(2B)=(s−c)tan(2C)
where a,b,c are sides, r is inradius, and s is semiperimeter
s=2a+b+c
Calculation:
Here, in triangle ABC, Let C=2π,
sinCc=2R
⇒2R=sin(π/2)c=c
R=2C
Now, inradius r=(s−c)tan(2C)
=(s−c)tan(4π)
=(s−c)
So, 2(r+R)=2(s−c+2C)=2(s−2C)
=a+b+c−c
=a+b
Hence, option (1) is correct.