Why are triangles to hard to find the angles to?

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mkcapen1's profile pic

mkcapen1 | Middle School Teacher | (Level 3) Valedictorian

Posted on

Finding the angles in a triangle is much easier if you use a protractor.  A protract enables you to measure the angle.  Angles have a range between 0 and 180 degrees.

Center the protractor on the tip of the angle you are measuring. 

Make sure the base line lines up with the bottom side of the angle that you are measuring.

Take a pencil and draw a line to the location where the center point goes straight to the top line of the angle at the top of the protractor.

Look at the number listed on the angle.

You will issue either the top set of degrees or the bottom set depending if the angle is obtuse or not.

Some things to remember:

·     All triangles measure at 180 degrees

·     A right angle measures at 90 degrees

·     If you have a right angel the other two angles will each measure at 45 degrees

·     An obtuse angle is larger than 90 degrees

·     a 90 degree angle looks like making an "L"



neela's profile pic

neela | High School Teacher | (Level 3) Valedictorian

Posted on

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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