# The criss-crossing angles that appeared when two parallel straight lines were cut by the third straight line add 80

**The criss-crossing angles that appeared when two parallel straight lines were cut by the third straight line add 80 degrees together. Find all the angles that appeared.**

The inner cross lying angles for parallel lines and secant are equal. If we know the sum of the interior angles lying crosswise, then to find one of them, we need to divide 80 degrees in half.

Let our angles be 3 and 6. Angle 3 = angle 6 = 80: 2 = 40 degrees.

Angle 3 and Angle 5 are internal one-sided angles, and their sum is 180 degrees. Angle 5 = 180 – 40 = 140 degrees.

Angles 5 and 4 are internal crosswise and they are equal. Angle 4 = 140 degrees.

Angles 2 and 3 and angles 6 and 7 are vertical and equal. Angle 3 = 40 degrees, angle 7 = 40 degrees.

Angles 1 and 4 and angles 5 and 8 are also vertical, and the vertical angles are equal. Angle 1 = 140 degrees, angle 8 = 140 degrees.

Answer. Angles 1, 4, 5, 8 are 140 degrees, angles 2, 3, 6, 7 are 40 degrees.