a) 24:x=24:2

⇒ x=2

b) 9:x>9:2

⇒ x<2

a) 2x+69.2=69.4

 ⇒ 2x+69.2=69.(2+2)

 ⇒ 2x+69.2=69.2+69.2

 ⇒2x=69.2

 ⇒ x=69

b) 2x-12-x=0

 ⇒ 3x-12=0

 ⇒ 3x=0+12=12

 ⇒ x=12:3

 ⇒ x=4

3^2x+6=9¹⁰

⇒ 3^2x+6=(3²)¹⁰

⇒ 3^2x+6=3^2.10

⇒ 3^2x+6=3²⁰

⇒ 2x+6=20

⇒ 2x= 20-6=14

⇒ x=14:2=7

\(-\dfrac{1}{2}x-\dfrac{9}{12}=0,25\\ \\ \Rightarrow-\dfrac{1}{2}x-\dfrac{3}{4}=\dfrac{1}{4}\\ \\ \Rightarrow-\dfrac{1}{2}x=\dfrac{1}{4}+\dfrac{3}{4}=1\\ \\ \Rightarrow x=1:\left(-\dfrac{1}{2}\right)=-2\)

\(\dfrac{3}{5}+\dfrac{7}{4}-\dfrac{8}{7}\\ \\ =\dfrac{12}{20}+\dfrac{35}{20}-\dfrac{8}{7}\\ \\ =\dfrac{35}{20}-\dfrac{8}{7}\\ \\ =\dfrac{7}{5}-\dfrac{8}{7}\\ \\ =\dfrac{49}{35}-\dfrac{40}{35}=\dfrac{9}{35}\)

\(A=\dfrac{2}{6}+\dfrac{2}{12}+\dfrac{2}{20}+...+\dfrac{2}{90}\\ \\ A=\dfrac{2}{2.3}+\dfrac{2}{3.4}+\dfrac{2}{4.5}+...+\dfrac{2}{9.10}\\ \\ A=2.\left(\dfrac{1}{2.3}+\dfrac{1}{3.4}+\dfrac{1}{4.5}+...+\dfrac{1}{9.10}\right)\\ \\ A=2.\left(\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{5}+...+\dfrac{1}{9}-\dfrac{1}{10}\right)\\ \\ A=2.\left(\dfrac{1}{2}-\dfrac{1}{10}\right)\\ \\ A=2.\left(\dfrac{5}{10}-\dfrac{1}{10}\right)\\ \\ A=2.\dfrac{2}{5}=\dfrac{4}{5}\\\)

. LÀ x

q=2²+4²+6²+...+18²

q= 1².2²+2².2²+3².2²+...+9².2²

q= 2².(1²+2²+3²+...+9²)

q= 2².285=4.285=1140

Hiệu ủa chúng là: 8x2=16

Số lớn là: (74+16):2=45

Số bé là: 74-45=29

    Đ/S:...