CK-12 Geometry-Concepts

http://www.ck12.org Chapter 4. Triangles and Congruence

Let’s start withy. Both sides are equal, so set the two expressions equal to each other and solve fory.

5 y− 1 = 2 y+ 11

3 y= 12

y= 4

Forx, we need to use two( 2 x+ 5 )◦expressions because this is an isosceles triangle and that is the base angle
measurement. Set all the angles equal to 180◦and solve.

( 2 x+ 5 )◦+( 2 x+ 5 )◦+( 3 x− 5 )◦= 180 ◦

( 7 x+ 5 )◦= 180 ◦

7 x= 175 ◦

x= 25 ◦

Example C

Two sides of an equilateral triangle are 2x+5 units andx+13 units. How long is each side of this triangle?

The two given sides must be equal because this is an equilateral triangle. Write and solve the equation forx.

2 x+ 5 =x+ 13

x= 8

To figure out how long each side is, plug in 8 forxin either of the original expressions. 2( 8 )+ 5 =21. Each side is
21 units.

Watch this video for help with the Examples above.

MEDIA

Click image to the left for use the URL below.

URL: http://www.ck12.org/flx/render/embeddedobject/52625

CK-12 Foundation: Chapter4EquilateralTrianglesB