Triangle and its exterior angle

[Guest]

The exterior angels of a triangle are 3y, 4y, and 5y. Find y.
What are the interior angels of the triangle.

[Guest]

The sum of the internal angles of a triangle is 180 degrees.
Internal angles are 180 - 3y
180 - 4y
180 - 5y



180 - 3y + 180 - 4y + 180 - 5y = 180

-3y - 4y - 5y = 180 - 180 - 180 - 180

-12y = -360

12y = 360

y = 30

[Guest]

Here are the interior angles of a triangle:

interior.gif (5.42 KiB) Viewed 2464 times

[leesajohnson]

=> 180 - 3y + 180 - 4y + 180 - 5y = 180

=> -3y - 4y - 5y = 180 - 180 - 180 - 180

=> -12y = -360

=> 12y = 360

=> y = 30