Step-by-step explanation:
(7m - 3)² = 49m² - 42m + 9
play it through and do the actual multiplication behind the square :
(7m - 3)² = (7m - 3)(7m - 3) =
= 7m×7m + 7m×(-3) + (-3)×7m + (-3)(-3) =
= 49m² - 2×21m + 9 = 49m² - 42m + 9
