Răspuns:
De unde ai ramas :
(a + 2 ) × 9 = 72
Prin metoda mersului invers 》 a + 2 = 72÷ 9
a + 2 = 8
a = 8 - 2 = 6
a + 9 = 6 + 9 = 15
a × 9 = 6 × 9 = 54
a × 9 = 45 》 a = 5
a + 9 = 5 + 9 = 14
(a+2) × 9 = 7 × 9 = 63
a = 3
a + 9 = 3 + 9 = 12
a × 9 = 3 × 9 = 27
( a + 2) × 9 = 5 × 9 = 45
a + 9 = 13 》 a = 13 - 9 = 4
a × 9 = 4 × 9 = 36
( a + 2 ) × 9 = 6 × 9 = 54
