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Oblique Triangle

Calculate oblique triangles.

An oblique triangle is any triangle that is not a right angled triangle.

Triangle Three Known Values - Length and Angle Calculator

Calculate the unknown lengths and angles in a triangle. Add three known values - leave the rest of the inputs blank.

Note! - the calculator is based on the same value combinations used in the equations below. Other value combinations will not work - most triangles with three known values can be adapted to these equations. The calculator is quite simple. With strange results - check your input values.

Area (m2, mm2, ft2, in2 .....):

(enable pop-up)

A, B and a is known, calculate

b = a sin(B) / sin(A)                       (1a)

C = 180o - (A + B)                        (1b)

c = a sin(C) / sin(A)                       (1c)

A, a and b is known, calculate

sin(B) = b sin(A) / a                      (2a)

C = 180o - (A + B)                      (2b)

c = a sin(C) / sin(A)                      (2c)

a, b and C is known, calculate

tan(A) = a sin(C) / (b - a cos(C))                 (3a)

B= 180o - (A + C)                        (3b)

c = a sin(C) / sin(A)                       (3c)

a, b and c is known, calculate

cos(A) = (b2 + c2 - a2) / (2 b c)                      (4a)

cos(B)= (a2 + c2 - b2) / (2 a c)                      (4b)

C = 180o - (A + B)                              (4c)

a, b, c, A, B and C is known, calculate area

s = (a + b + c) / 2                        (5a)

area = (s (s - a) (s- b) (s - c))1/2                     (5b)

area = b c sin(A) / 2                           (5c)

area = a2 sin(B) sin(C) / (2 sin(A))                     (5d)

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Citation

• The Engineering ToolBox (2014). Oblique Triangle. [online] Available at: https://www.engineeringtoolbox.com/oblique-triangle-formulas-d_1871.html [Accessed Day Month Year].

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6.3.17

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