Beginning Algebra, 11th Edition

Triangles and Angles

Right Angle

Measure is 90°.

Right Triangle

Triangle has one 90°
(right) angle.

Pythagorean Theorem
( for right triangles)

a^2 +b^2 =c^2

Isosceles Triangle

Two sides are equal.

AB=BC

Straight Angle

Measure is 180°.

Equilateral Triangle

All sides are equal.

AB=BC=CA

Complementary Angles

The sum of the measures of

two complementary

angles is 90°.

Sum of the Angles of Any Triangle

A+B+C=180°

Supplementary Angles

The sum of the measures

of two supplementary

angles is 180°.

Similar Triangles

Corresponding angles are
equal. Corresponding sides
are proportional.

AB

DE

=

AC

DF

=

BC

EF

A=D, B=E, C=F

Vertical Angles

Vertical angles have

equal measures.

A C

B

a c

b

90 °

A C

B

A

B

C

A

C

B

E

F

D

2

4

1 3

Angle 1 = Angle 3

Angle 2 = Angle 4

180 °

2

1

Angles 1 2

are complementary.

and

3 4

Angles 3 and 4 are supplementary.