A triangle has sides with lengths of 5, 7, and 3. What is the radius of the triangles inscribed circle?

1 Answer
Oct 27, 2016

Radius =sqrt(3)/2

Explanation:

[1] Step 1: Find the Area of the Triangle
Use Heron's formula: Area_triangle=sqrt(s(s-a)(s-b)(s-c))
where a, b, c are the lengths of the sides and s is the semi-perimeter (a+b+c)/2

color(white)("XXX")s=(5+7+3)/2=15/2

color(white)("XXX")Area_triangle = sqrt(15/2 * 5/2 * 1/2 * 9/2)

color(white)("XXXXXXX")=15/4sqrt(3)

[2] Step 2: Find the Radius of Inscribed Circle
Use teh forumla: "Radius"_circ = "Area"_triangle/s
color(white)("XXXXXXXXX")If you are unfamiliar with this formula:
color(white)("XXXXXXXXX")ask to have it explained as a separate question.

color(white)("XXX")r_circ = (15/4sqrt(3))/(15/2)=sqrt(3)/2

~~~~~~ Oops! The next step wasn't asked for but I did it anyway ~~~~~
[3] Calculate the Area of the Circle
Use the formula: "Area"_circ = pir^2

color(white)("XXX")"Area"_circ = pi(sqrt(3)/2)^2=3/4pi