(x - 4)(x + 2) ≤ 0

⇒ x - 4 ≤ 0 và x + 2 > 0

*) x - 4 ≤ 0

x ≤ 0 + 4

x ≤ 4

*) x + 2 > 0

x > 0 - 2

x > -2

Vậy -2 ≤ x ≤ 4

D = 1 + 3² + 3⁴ + ... + 3⁹⁸ + 3¹⁰⁰

⇒ 9D = 3² + 3⁴ + 3⁶ + ... + 3¹⁰⁰ + 3¹⁰²

⇒ 8D = 9D - D

= (3² + 3⁴ + 3⁶ + ... + 3¹⁰⁰ + 3¹⁰²) - (1 + 3² + 3⁴ + ... + 3⁹⁸ + 3¹⁰⁰)

= 3¹⁰² - 1

⇒ D = (3¹⁰² - 1) : 8

\(D=1+3^2+3^4+...+3^{98}+3^{100}\)

=>\(9D=3^2+3^4+...+3^{102}\)

=>\(9D-D=3^2+3^4+...+3^{102}-1-3^2-...-3^{98}-3^{100}\)

=>\(8D=3^{102}-1\)

=>\(D=\dfrac{3^{102}-1}{8}\)

(x . 627 + 37 ) . 215 = ( -2  ) + 37

( x . 627 + 37) . 215 = 35

( x . 627 + 37)          = 35 : 215

( x . 627 + 37)          = 7/43

x . 627 = 7/43 - 37

x . 627 = - 1584/43

x          = -1584/43 : 627

x          = -48/817

Vậy x = - 48/817

(x . 627 + 37 ) . 215 = ( -2  ) + 37

( x . 627 + 37) . 215 = 35

( x . 627 + 37)          = 35 : 215

( x . 627 + 37)          = 7/43

x . 627 = 7/43 - 37

x . 627  = - 1584/43

x          = -1584/43 : 627

x          = - 48/817

  Vậy x = - 48/817

a: \(\dfrac{-2}{9}+\dfrac{8}{15}+1\dfrac{2}{3}-\dfrac{7}{9}+\dfrac{-7}{-15}\)

\(=\left(-\dfrac{2}{9}-\dfrac{7}{9}\right)+\left(\dfrac{8}{15}+\dfrac{7}{15}\right)+\dfrac{5}{3}\)

\(=-1+1+\dfrac{5}{3}=\dfrac{5}{3}\)

b: \(\dfrac{2}{7}\cdot10\dfrac{2}{8}-\dfrac{2}{7}\cdot3\dfrac{1}{4}\)

\(=\dfrac{2}{7}\left(10+\dfrac{1}{4}-3-\dfrac{1}{4}\right)\)

\(=\dfrac{2}{7}\cdot7=2\)

c: \(\dfrac{5}{7}+\dfrac{2}{7}:0,25-0,4\)

\(=\dfrac{5}{7}+\dfrac{2}{7}\cdot4-\dfrac{2}{5}\)

\(=\dfrac{5}{7}+\dfrac{8}{7}-\dfrac{2}{5}=\dfrac{13}{7}-\dfrac{2}{5}=\dfrac{65-14}{35}=\dfrac{51}{35}\)

\(B=\dfrac{n+1}{n-2}=\dfrac{n-2+3}{n-2}=\dfrac{n-2}{n-2}+\dfrac{3}{n-2}=1+\dfrac{3}{n-2}\)

Để B nguyên

\(\Rightarrow3⋮n-2\) 

\(\Rightarrow n-2\inƯ\left(3\right)=\left\{1;3;-1;-3\right\}\)

\(\Rightarrow n\in\left\{3;5;1;-1\right\}\)

Sửa đề: Tìm n nguyên để B nguyên

ĐKXĐ: n<>2

Để B nguyên thì \(n+1⋮n-2\)

=>\(n-2+3⋮n-2\)

=>\(3⋮n-2\)

=>\(n-2\in\left\{1;-1;3;-3\right\}\)

=>\(n\in\left\{3;1;5;-1\right\}\)

\(D=\dfrac{1}{49}+\dfrac{2}{48}+\dfrac{3}{47}+...+\dfrac{49}{1}\)

\(D=\dfrac{1}{49}+1+\dfrac{2}{48}+1+....+\dfrac{48}{2}+1+1\)

\(D=\dfrac{50}{49}+\dfrac{50}{48}+....+\dfrac{50}{2}+\dfrac{50}{50}\)

\(D=50\left(\dfrac{1}{49}+\dfrac{1}{48}+...+\dfrac{1}{2}+\dfrac{1}{50}\right)\)

\(\Rightarrow\dfrac{C}{D}=\dfrac{\dfrac{1}{2}+\dfrac{1}{3}+...+\dfrac{1}{50}}{50\left(\dfrac{1}{49}+\dfrac{1}{48}+...+\dfrac{1}{50}\right)}=\dfrac{1}{50}\)

cám ơn

Bạn bổ sung đề bài chỗ "cứ ... m² thì thu được" là bao nhiêu nhé.

a: Số tiền ông Bách nhận được sau 1 năm là:

\(100000000\left(1+7,3\%\right)=107300000\left(đồng\right)\)

b: Số tiền ông Bách nhận được sau 2 năm là:

\(107300000\left(1+7,3\%\right)=115132900\left(đồng\right)\)