a, 97 . 103 = ( 100 - 3 ) . ( 100 + 3 ) = 100² - 3² = 10000 - 9 = 9991
b, 77² + 23² + 77 . 46 = 77² + 23² + 2 . 23 . 77 = ( 77 + 23 )² = 100² = 10000
c, 892² + 892 . 216 + 108² = 892² + 2 . 892 . 108 + 108² = ( 892 + 108 )² + 1000² = 1000000
d, 36² + 26² - 52 . 36 = 36² + 26² - 2 . 26 . 36 = ( 36 - 26 )² = 10² = 100