In this video you will be shown how to work out missing sides in right angled isosceles triangles. So in example 1 you are given two sides, each 7cm long, and you need to find the hypotenuse. To do this square the two sides and add them together as you are working out the longest side. 7 squared is 49, and 49 doubled is 98. The square root of 98 is 9.9cm.
In example 2, you are given the hypotenuse of 11cm and you need to find the lengths of the shorter sides. To do this set up the equation 2y^2=121. Solve this equation by dividing 121 by 2 which is 60.5, and then take the square root to give 7.8cm.