# 11 18 21 triangle

### Acute scalene triangle.

Sides: a = 11   b = 18   c = 21

Area: T = 98.99549493661
Perimeter: p = 50
Semiperimeter: s = 25

Angle ∠ A = α = 31.58663380965° = 31°35'11″ = 0.55112855984 rad
Angle ∠ B = β = 58.99224169931° = 58°59'33″ = 1.03296119102 rad
Angle ∠ C = γ = 89.42112449103° = 89°25'16″ = 1.56106951449 rad

Height: ha = 17.99990817029
Height: hb = 10.99994388185
Height: hc = 9.42880904158

Median: ma = 18.76883243791
Median: mb = 14.14221356237
Median: mc = 10.59548100502

Inradius: r = 3.96597979746
Circumradius: R = 10.50105357006

Vertex coordinates: A[21; 0] B[0; 0] C[5.66766666667; 9.42880904158]
Centroid: CG[8.88988888889; 3.14326968053]
Coordinates of the circumscribed circle: U[10.5; 0.10660660172]
Coordinates of the inscribed circle: I[7; 3.96597979746]

Exterior(or external, outer) angles of the triangle:
∠ A' = α' = 148.4143661903° = 148°24'49″ = 0.55112855984 rad
∠ B' = β' = 121.0087583007° = 121°27″ = 1.03296119102 rad
∠ C' = γ' = 90.57987550897° = 90°34'44″ = 1.56106951449 rad

# How did we calculate this triangle?

Now we know the lengths of all three sides of the triangle and the triangle is uniquely determined. Next we calculate another its characteristics - same procedure as calculation of the triangle from the known three sides SSS. ### 1. The triangle circumference is the sum of the lengths of its three sides ### 2. Semiperimeter of the triangle ### 3. The triangle area using Heron's formula ### 4. Calculate the heights of the triangle from its area. ### 5. Calculation of the inner angles of the triangle using a Law of Cosines ### 6. Inradius ### 7. Circumradius ### 8. Calculation of medians #### Look also our friend's collection of math examples and problems:

See more informations about triangles or more information about solving triangles.