8x + 2 = 18

8x = 18 - 2 

8x = 16

x = 16 : 8

x = 2

(20.2⁴+12.2^4_48.2²)÷8²

=(20.16+12.16-48.4)÷64

={[16.(20+12)]-48.4}÷64

=(16.32-48.4)÷64

=(512-192)÷64=320÷64=5

Chu vi hình vuông là :

20 + 20 + 20 +20 = 20 x 4 = 80 (cm)

Đáp số : 80 cm

\(K=\frac{1}{2}.\left(\frac{2}{1.3}+\frac{2}{3.5}+..........+\frac{2}{47.49}\right)\)

\(=\frac{1}{2}.\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+........+\frac{1}{47}-\frac{1}{49}\right)\)

\(=\frac{1}{2}.\left(1-\frac{1}{49}\right)\)

\(=\frac{1}{2}.\frac{48}{49}\)

\(=\frac{24}{49}\)

x + 10 = 30 

x         = 30 - 10 

x         = 20

19 + 4 = 23

20 + 5 = 25

74 + 3 = 77

obrigado