The Square Mark

Part of the Angles section of Coddy's Geometry journey. Lesson 12 of 63.

A right angle often carries no number at all, only the small square in its corner. That square is a measure like any label: it says 90°. When you need the angle's size, you read it off the square.

$A straight line with three angles: 35 degrees, a right angle marked with a square, and 55 degrees$

Here three angles fill the straight line PQ. The middle one has the square, so it is 90°, and the three add up to 180°: 35 + 90 + 55 = 180. If the 55° were missing, you would first say the middle angle is 90°, then take 35 and 90 away from 180.

That is two steps on the figure. Tap the square angle and pick Right angle: its 90° appears. Now the angle you want has every neighbour known, and Angles on a straight line finishes it.

Challenge

Two rays stand on the straight line PQ, and one of the three angles carries a square. Find the angle marked ?: give every step its rule, then press Check.

Try it yourself

$Find the marked part of the figure$