\(3\times\left(x-2\right)+9=30\)

\(3\times\left(x-2\right)=30-9\)

\(3\times\left(x-2\right)=21\)

\(x-2=7\)

\(x=9\)

\(3.\left(x-2\right)+9=30\)

\(\Leftrightarrow3x-6+9=30\)

\(\Leftrightarrow3x=27\)

\(\Leftrightarrow x=9\)

Bạn cần bài nào thì nên ghi chú rõ bài đó ra.

\(\left(x+9\right)+\left(x-2\right)+\left(x+7\right)+\left(x-4\right)+\left(x+5\right)+\left(x-6\right)+\left(x+3\right)+\left(x-8\right)+\left(x+1\right)=95\)

\(x+9+x-2+x+7+x-4+x+5+x-6+x+3+x-8+x+1=95\)

\(\left(x\times9\right)+\left(9-2+7-4+5-6+3-8+1\right)=95\)

\(x\times9+5=95\)

\(x\times9=95-5\)

\(x\times9=90\)

\(x=90:9\)

\(x=10\)

(x + 9) + (x - 2) + (x + 7) + (x - 4) + (x + 5) + (x - 6) + (x + 3) + (x - 8) + (x + 1) = 95

x + 9 + x - 2 + x + 7 + x - 4 + x + 5 + x - 6 + x + 3 + x - 8 + x + 1

(x + x + x + x + x + x + x + x + x) + (9 - 8 + 7 - 6 + 5 - 4 + 3 - 2 + 1) = 95

9 × x + 5 = 95

9 × x = 95 - 5

9 × x = 90

x = 90 : 9

x = 10

\(\dfrac{x}{2013}\) - \(\dfrac{1}{10}\) - \(\dfrac{1}{15}\) - \(\dfrac{1}{21}\)-...-\(\dfrac{1}{120}\) = \(\dfrac{5}{8}\)

(\(\dfrac{x}{2013}\) - \(\dfrac{1}{10}\) - \(\dfrac{1}{15}\) - \(\dfrac{1}{21}\)-...- \(\dfrac{1}{120}\))\(\times\)\(\dfrac{1}{2}\) = \(\dfrac{5}{8}\)\(\times\)\(\dfrac{1}{2}\)

\(\dfrac{x}{4026}\) - \(\dfrac{1}{20}-\dfrac{1}{30}-\dfrac{1}{42}-...-\dfrac{1}{240}\) = \(\dfrac{5}{16}\)

\(\dfrac{x}{4026}\) - (\(\dfrac{1}{20}+\dfrac{1}{30}+\dfrac{1}{42}+...+\dfrac{1}{240}\)) = \(\dfrac{5}{16}\)

\(\dfrac{x}{4026}\) - (\(\dfrac{1}{4\times5}\)+ \(\dfrac{1}{5\times6}\)+\(\dfrac{1}{6\times7}\)+...+\(\dfrac{1}{15\times16}\)) = \(\dfrac{5}{16}\)

\(\dfrac{x}{4026}\) - (\(\dfrac{1}{4}\) - \(\dfrac{1}{5}\) + \(\dfrac{1}{5}\) - \(\dfrac{1}{6}\) + \(\dfrac{1}{6}\) - \(\dfrac{1}{7}\)+...+ \(\dfrac{1}{15}\) - \(\dfrac{1}{16}\)) = \(\dfrac{5}{16}\)

\(\dfrac{x}{4026}\) - (\(\dfrac{1}{4}\) - \(\dfrac{1}{16}\)) = \(\dfrac{5}{16}\)

\(\dfrac{x}{4026}\) = \(\dfrac{5}{16}\) +( \(\dfrac{1}{4}\) - \(\dfrac{1}{16}\))

\(\dfrac{x}{4026}\) = \(\dfrac{5}{16}\) + \(\dfrac{3}{16}\)

\(\dfrac{x}{4026}\) = \(\dfrac{8}{16}\)

\(\dfrac{x}{4026}\) = \(\dfrac{1}{2}\)

\(x\) = \(\dfrac{1}{2}\) \(\times\) 4026

\(x\) =  2013

a) 53,2 : (X - 3,5) + 45,8 = 99

53,2 : (X - 3,5) = 99 - 45,8

53,2 : (X - 3,5) = 53,2

X - 3,5 = 53,2 : 53,2

X - 3,5 = 1

X = 1 + 3,5

X = 4,5

--------------------

b) 71 + 65 × 4 = (X + 140)/X + 260

(X + 140)/X + 260 = 331

(X + 140)/X = 331 - 260

(X + 140)/X = 71

X + 140 = 71 × X

71 × X - X = 140

70 × X = 140

X = 140 : 2

X = 70

1) (455 - x : 2 × 6) : 5 = 31

455 - x : 2 × 6 = 31 × 5

455 - x : 2 × 6 = 155

x : 2 × 6 = 455 - 155

x : 2 × 6 = 300

x : 2 = 300 : 6

x : 2 = 50

x = 50 × 2

x = 100

--------------------

2) (674 - 23 × 23) : x × 2 = 58

(674 - 529) : x × 2 = 58

145 : x × 2 = 58

145 : x = 58 : 2

145 : x = 29

x = 145 : 29

x = 5

--------------------

3) 235 - x × 5 + 365 = x × 35

(235 + 365) - x × 5 = x × 35

600 - x × 5 = x × 35

x × 35 + x × 5 = 600

x × 40 = 600

x = 600 : 40

x = 15

--------------------

4) 674 + x : 3 × 18 - x × 46 = 541

674 + x × 1/3 × 18 - x × 46 = 541

x × 46 - x × 6 = 674 - 541

x × 40 = 133

x = 133 : 40

x = 3,325

--------------------

5) (x × 24) : (x × 4) = 132 - (x × 7)

6 = 132 - (x × 7)

x × 7 = 132 - 6

x × 7 = 126

x = 126 : 7

x = 18

(1/15 + 1/35 + 1/63) × x = 1

(21/315 + 9/315 + 5/315) × x = 1

35/315 × x = 1

1/9 × x = 1

x = 1 : 1/9

x = 9

` @ L I  N H `

(1/15 + 1/35 + 1/63) × x = 1

(21/315 + 9/315 + 5/315) × x = 1

35/315 × x = 1

1/9 × x = 1

x = 1 : 1/9

x = 9

tổng độ dài 2 đáy:

  2x25=50(cm)

độ dài chiều cao hình thang

  100:50=2(cm)

tổng đọ dài 2 đáy sau khi tăng:

   50 + 15=65(cm)

diện tích hình thang sau khi tăng

  65 x 2=130(cm2)

                    Đáp số:130cm2

Chúc bạn học giỏi.Thi đỗ Trần Đăng Ninh.

Diện tích hình thang tăng thêm là bao nhiêu thế em?

vì gọi a/b là phân số cần tìm 

nếu cộng 2 ta có : (a+2)/b= 1 =>a+2= b

nếu cộng 3 ta có a/(b+3) =1/2 => 2a=b+3 

thay b vào 2a=b+3 =>a= 7

thay a vào => b= 11

nhớ tick với nhé !!!!!!!!!!<3