What you need: ruler, protractor, pencil and paper. Use these to construct a triangle when you know the length of 1 side and the 2 angles at each end of it. In this case use the length 8 cm ...

Place the centre of the protractor on the end of the line and mark 40° with a dot. Image caption, STEP 2: Use a ruler to draw a line from the end of the line through the dot and label the angle 40°.

Changing the ruler’s 0 origin means changing ... the tool to 45° increments. To create a protractor from an existing measuring line, Alt-drag at an angle from one end of the measuring line.