Determine the circle radius if the circle is inscribed in a triangle wich has the sides lenghts of 13, 14, and 15 .

4 Answers | Add Yours

hala718's profile pic

hala718 | High School Teacher | (Level 1) Educator Emeritus

Posted on

Let A be the area of the triangle

P be the perimeter of the tirangle

and r is the radius of the circlr:

Then, we know that:

   A = r * P/2

Let us caclculateL

P = 13 + 14 + 15 = 42

==> p/2 = 42/2 = 21

Now for A:

A =sqrt[ p/2 (p/2- 13)(p/2 - 14)(p/2 - 15)]

     = sqrt[21*8*7*6]

     = 84

Then:

 A = r* p/2

84 = r * 21

==> r= 84/21= 4

Then the radius = 4 units

 

neela's profile pic

neela | High School Teacher | (Level 3) Valedictorian

Posted on

We have area  A of the triangle = sqrt{s(s-a)(s-b)s-c)}

a = 1, b =14, c 15

Therefore  s= (13+14+15)/2 = 42/2 = 21.

Area = sqrt{21(21-13)(21-14)21-15)} = sqr(21*8*7*6} =  84.

Also area of the triangle = (1/2) (a+b+c)r = 84.

Therefore , (1/2)(42)r = 84

r = 84*2/42 = 4.

giorgiana1976's profile pic

giorgiana1976 | College Teacher | (Level 3) Valedictorian

Posted on

If we know the lengths of the triangle sides, we could calculate the radius with the help of the following formula: R=S/p, where R-radius, S-aria of the triangle and p-semi-perimeter of the triangle.

p=(13+14+15)/2=21

S= sq root [21(21-13)(21-14)(21-15)]=84

R=84/21=4

william1941's profile pic

william1941 | College Teacher | (Level 3) Valedictorian

Posted on

We have to find the radius of the circle inscribed in a triangle with sides of length 13, 14 and 15.

Now we have the area of a triangle given as sqrt [ s ( s-a) (s-b) (s-c)] and it is also equal to r*s where s is the semi perimeter and r is the radius of the inscribed circle.

So r*s =  sqrt [ s ( s-a) (s-b) (s-c)]

r = sqrt [ s ( s-a) (s-b) (s-c)] / s  = sqrt [( s-a) (s-b) (s-c)]/ s ].

As the sides are 13, 14 and 15, the semi perimeter s = 21 .

So substituting we get r = sqrt [ 8* 7* 6 / 21] = sqrt 16 = 4.

So the required radius is 4

We’ve answered 318,912 questions. We can answer yours, too.

Ask a question