 Do you like triangles?

# Triangles and Angles

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A triangle is a geometric form created by connecting three straight lines. Where each line connects or intersects you get an angle. A triangle will have three angles.

An angle is measured in degrees (°). The degree of an angle runs between 0° and 180°.

Both triangles and angles are classified into three different types: acute, right and obtuse

TRIANGLES:

An acute triangle is a triangle where all three angles measure less than 90°.
Example: Angle A is 47°, Angle B is 39°, and Angle C is 12°

A right triangle is a triangle where at least one of the angles measures exactly 90°.
Example: Angle A is 68°, Angle B is 51°, and Angle C is 90°

An obtuse triangle is a triangle where at least one of the angles measures more than 90°.
Example: Angle A is 22°, Angle B is 138°, and Angle C is 44°

ANGLES:

An acute angle is an angle that measures less than 90°.
A right angle is an angle that measures exactly 90°.
An obtuse angle is an angle that measures more than 90°.

How to find the missing degree of an angle in a triangle is easy. You need to subtract the known from the sum of the three angles. If Angle A is 92° and Angle B is 31° what would Angle C be? You simply start with Angle A and subtract Angle B to get Angle C as follows:

92° - 31° = 61°

Angle C is 61° - correct? Well, not exactly because, remember, we are measuring the degree of an angle of a triangle. The three angles of a triangle must always be equal to a total of 180° (the sum of all three angles). So we need to first add together the known angles, here it is 92° and 31° and then we subtract that answer from the total of 180° as follows:

92° + 31° = 123°
180° - 123° = 57°
92° + 31° + 57° = 180°
Angle C = 57°

1.
What type of a triangle do you have if Angle A is 28°, Angle B is 62°, and Angle C is 90°?
Right
Acute
Obtuse
Straight
When at least one angle measures exactly 90°, it is a right triangle. Answer (a) is correct
2.
If Angle A is 68° and Angle B is 22°, what type of an angle would Angle C be?
Acute
Right
Straight
Obtuse
68° + 22° = 90°
180° - 90° = 90°
Angle C is 90° making it a right angle so Answer (b) is the correct answer
3.
If Angle A is 49° and Angle B is 27°, what type of an angle would Angle C be?
Obtuse
Right
Acute
Straight
49° + 27° = 76°
180° - 76° = 104°
Angle C is 104° and because it is greater than 90° it is an obtuse. Answer (a) is the correct answer
4.
What type of triangle do you have if Angle A is 13°, Angle B is 45°, and Angle C is 122°?
Straight
Obtuse
Right
Acute
When at least one angle is more than 90°, it is an obtuse triangle. Answer (b) is correct
5.
What type of a triangle do you have if Angle A is 56°, Angle B is 111°, and Angle C is 13°?
Straight
Right
Acute
Obtuse
When at least one angle is more than 90°, it is an obtuse triangle. Answer (d) is correct
6.
What type of a triangle do you have if Angle A is 77°, Angle B is 82°, and Angle C is 21°?
Acute
Right
Obtuse
Straight
When all three angles are less than 90°, it is an acute triangle. Answer (a) is correct
7.
What is Angle C of a triangle if Angle A is 67° and Angle B is 59°?
126°
54°
113°
121°
67° + 59° = 126°
180° - 126° = 54°
67 + 59 + 54 = 180°
Angle C is 54° so Answer (b) is correct
8.
If Angle A is 60° and Angle B is 45°, what type of an angle would Angle C be?
Straight
Obtuse
Acute
Right
60° + 45° = 105°
180° - 105° = 75°
Angle C is 75° and because it is less than 90° it makes it an acute angle. Answer (c) is the correct answer
9.
What is Angle C if Angle A is 33° and Angle B is 17°?
147°
163°
50°
130°
33° + 17° = 50°
180° - 50° = 130°
10.
If Angle A is 72° and Angle B is 33°, what type of an angle would Angle C be in a triangle?
Right
Straight
Obtuse
Acute
72° + 33° = 105°
180° - 105° = 75°
Angle C is 75° and because it is less than 90° it is an acute angle. Answer (d) is the correct answer
Author:  Christine G. Broome