Hello. Firstly you have to remembet that the sum of the three angles in any triangle is 180grades So, determining the constant (k) you will have: 2:9:1 2k+9k+1k=180 12k=180 180/12=k k = 15 Multiply the constant by 180 and divide by the given ratio: 180*15 / 2 180*15 / 9 etc then your angles are 2:9:1 24:108:12