Math formula for class 7. Math formula for class 10. Math formula for class 7. A 4 b 4 a b a b a 2 b 2 a 5 b 5 a b a 4 a 3 b a 2 b 2 ab 3 b 4 परकतक सखय Natural Numbers a n b n a b a n-1 a n-2 b n-2 a b n-1 सम सखय Even n 2k a n b n a b a n-1 a n-2 b b n-2 a b n-1.