Constructing triangles GM3.2 Extension Plenary This is activity is about estimating lengths and angles. You do not need a ruler or protractor. Make a rough scaled sketch of each of these. A triangle ABC, where AC = 4 cm, BC = 7 cm and ACB is a right angle. Estimate AB and ABC. A triangle RST, where RS = 6 cm, TRS = 30 and RST = 45. Estimate ST. Make up some similar questions to test a partner, but make sure you have drawn and measured the triangles so you know the correct answers. Preamble The aim of these problems is to give pupils practice in applying the construction techniques just learned, in the context of estimating angles and lengths. Sketching constructions from given information and estimating are useful skills which need regular practice. Pupils could perhaps check each other’s sketches/answers. Given sufficient time, more examples may be made up and the sketches/estimates performed. Possible content Using construction methods, estimating lengths and angles, using angle notation. Resources None (ruler and protractors only for checking final answers – not for sketching). Solution/Notes AB is between 7 cm and 9 cm. ABC is between 25 and 35. ST is between 2 cm and 4 cm.