`r = sqrt(( "a" + "b" + "c" )/2(( "a" + "b" + "c" )/2- "a" )(( "a" + "b" + "c" )/2- "b" )(( "a" + "b" + "c" )/2- "c" )) / (( "a" + "b" + "c" )/2)`

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The Radius of a Circle  within a Triangle formula computes Circle within a Triangle  the radius of circle (r) that is perfectly inscribed within a triangle. 

INSTRUCTIONS:  Choose units and enter the following:

• (a) This is the length of side a.
• (b) This is the length of side b.
• (c) This the length of side c.

Radius (r): The calculator returns the radius (r) of the circle the that could be inscribed within the triangle in meters. However, this can be automatically converted to other length units (e.g. feet) via the pull-down menu.

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Circle Calculators

• Circle Area -  Computes the area of a circle given the radius (A = π r²).
• Area of Circle Arc Segment f(r,θ) - Computes the area of an arc segment of a circle given the radius (r) and angle (θ)
• Area of Circle Arc Segment Area f(r,h) - Computes the area of an arc segment of a circle given radius (r) and the depth (h) into the circle.
• Area of Circle Sector f(r,Θ) - Computes the area of a sector (pie slice) of a circle given the radius (r) and angle (Θ).
• Angle of Circle Sector f(r,h) - Computes the angle in a circle from the radius and depth of the chord.
• Area of Circle Annulus - Computes the area of an annulus (ring) given the inner radius (r) and outer radius (R).
• Radius of Circle from Center and a Point - Computes the radius of a circle given the center point (h,k) and any other point (x,y) on the circle.
• Circumference of Circle -  Computes the circumference of a circle given the radius (C = 2 π r).
• Circle Arc Length - Computes the length of an arc length on a circle given the radius (r) and angle (Θ)
• Circle within a Triangle - Computes the radius of a circle inscribed within a triangle given the length of the three sides (a,b,c) of the triangle.
• Circle around a Triangle - Computes the radius of a circle that circumscribes a triangle given the length of the three sides (a,b,c) of the triangle.
• Circle Diameter from Area - Computes the radius and diameter of a circle from the area. 
• Circle Radius from Circumference - Computes the radius of a circle given the circumference.
• Circle Circumference from Area - Computes the circumference of a circle given the area.
• Circle Radius from Area - Computes the radius of a circle given the area.
• Chord Length: Computes the length of a chord in a circle from the radius and height.
• Circle Radius from Chord - Computes the radius of a circle based on the length of a chord and the chord's center height.
• Equation of Circle from Center and Point Coordinates - Develops the general equation of a circle based on the coordinates of the center (h,k) and any point on the circle (x,y).
• Circle with same Perimeter as an Ellipse - Computes the radius of the circle with the same perimeter of an ellipse defined by the semi-major and semi-minor axes.
• Rectangles to Cover a Circle - Computes the number of rectangles needed to minimally cover a circle based on the circle's diameter and the length and width of the rectangles.