A triangle has sides of length 8 cm, 10 cm and 14 cm. Work out the size of the largest angle of the triangle. Give your answer correct to 1 decimal place.

Utilising the cosine rule: c² = a² + b² - 2abcosC, substitute in the given lengths. We therefore get that 14² = 10² + 8² − 2 × 10 × 8 × cosA . Expanding this expression we then get that 196 = 164 - 160cosA. Then, rearranging the equation gives us that cosA = -1/5. Inputting this into the calculator gives us that A = 101.5 degrees (to one decimal place). We know that this is the largest angle in the triangle since the sum of the angles in a triangle is 180 degrees. 101.5 > 78.5, therefore the answer is correct.