There are two types of triangle that you might be required to construct using a ruler and protractor. The first type is where you are given two sides and the included angle (SAS).

Using a protractor, measure an angle of 40⁰ on the right-hand endpoint of the 9 cm line (to match the original triangle), mark it with a cross and draw a line.

From there, surveyors eye the summit and measure the angle with the assistance of a glorified, highly accurate protractor — a telescopic device known as a theodolite.