Question

(9-b)(b+9)+(4-b) в квадрате = 0

Answer 1

(9-b)(b+9) + (4-b)² = 0
9b + 81- 9b - b² = 0
81 - b² = 0
b² - 81 = 0
b² = 81
b =  -9; 9.