There are three angles of a triangle . Measuring the angle of a triangle is just like measuring angles between any two intersecting lines or rays, with the help of a protractor which is a semicircular graded for each degree. The angle between two lines is a measure of rotation required bring two lines or rays to coincide in the same postion.
In a triangle you can find the measure of angle between two lines by (i) actually measring the angle using protractor or (i) using the lengths of the sides using the relation between angles and sides or angles and area:
Depending on the type of easily measured values you could use one of the formula below to find the angle.
a/sinA =b/sinB=c/sinC
Area of the triangle = (1/2) bcsinA and similar formula or
cosC = (a^2+b^2-c^2}/(2ab)
Example: In a triangle the sides are : a=5, b=6, c=7 what are
the angles:
We use cosA = (b^2+c^2-a^2)/(2bc) =(6^2+7^2-5^2)/(2*6*7) = 0.7143
A=arc cos (0.7143)
So A =44.42 deg
B = arc cos (5^2+7^2-6^2)/(2*5*7)
= 57.12 deg and
C= arc cos(5^2+6^2-7^2/(2*5*6)
=78.46 deg.
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