Tìm x ∈ N, biết: a) (x - 3) : 2 = 5^14 : 5^12 b) 4x + 3x = 30 – 20 : 10 a) (x - 3) : 2

a) (x - 3) : 2 = 514 : 512

(x - 3) : 2 = 52

(x - 3) : 2 = 25

(x - 3) = 25.2

x = 50 + 3

x = 53

b) 4x + 3x = 30 – 20 : 10

7x = 30 - 2

7x = 28

x = 28 : 7

x = 4