Angles by cosine law

Calculate the size of the angles of the triangle ABC, if it is given by: a = 3 cm; b = 5 cm; c = 7 cm (use the sine and cosine theorem).

Correct result:

A =  21.7868 °
B =  38.2132 °
C =  120 °

Solution:

a=3 b=5 c=7 A1=arccos((b2+c2a2)/(2 b c))=arccos((52+7232)/(2 5 7))0.3803 A=A1=A1 180π=0.3803 180π=21.787=21.7868=214712"

Try calculation via our triangle calculator.

B1=arccos((a2+c2b2)/(2 a c))=arccos((32+7252)/(2 3 7))0.6669 B=B1=B1 180π=0.6669 180π=38.213=38.2132=381248"
C=180AB=18021.786838.2132=120



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Tips to related online calculators
Cosine rule uses trigonometric SAS triangle calculator.
See also our trigonometric triangle calculator.
Pythagorean theorem is the base for the right triangle calculator.

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