№1.
а) 7×98-636:6 = 686-106 = 580
б) (167+238)×39:117 = 405×39:117 = 15795:117 = 135
№2.
а) 35×с×8 = 280×с = 280с
б) у×450×4 = у×1800 = 1800у
№3.
а) 26520:m = 65
m = 26520:65
m = 408
б) 4z-22 = 26
4z = 26+22
4z = 48
z = 48:4
z = 12
№5.
x×х-1 = 15
x²-1 = 15
х² = 15+1
х² = 16
х = √16
х = 4
Проверка:
4×4-1 = 15
16-1 = 15
15=15