‘?’ द्वारा अंकित लुप्त पद ज्ञात कीजिये।

Each row is a Pythagorean triple: 13² = 12² + 5², 17² = 15² + 8² and 29² = 21² + 20². For the third row, 25² − 24² = 625 − 576 = 49 = 7², so the missing number is 7.