a) \(3\left(x-5\right)+6=36\)

\(\Rightarrow3\cdot\left(x-5\right)=36-6\)

\(\Rightarrow3\cdot\left(x-5\right)=30\)

\(\Rightarrow x-5=10\)

\(\Rightarrow x=10+5\)

\(\Rightarrow x=15\)

b) \(200-8\cdot\left(x+7\right)=24\)

\(\Rightarrow8\cdot\left(x+7\right)=200-24\)

\(\Rightarrow8\cdot\left(x+7\right)=176\)

\(\Rightarrow x+7=\dfrac{176}{8}\)

\(\Rightarrow x+7=22\)

\(\Rightarrow x=22-7\)

\(\Rightarrow x=15\)

c) \(\left(x-890\right)\left(74-x\right)=0\)

+) \(x-890=0\)

\(\Rightarrow x=890\)

+) \(74-x=0\)

\(\Rightarrow x=74\)

d) \(\left(31-x\right)\cdot\left(x-64\right)=0\)

+) \(31-x=0\)

\(\Rightarrow x=31\)

+) \(x-64=0\)

\(\Rightarrow x=64\)

\(\left(6:3,5-1\dfrac{1}{6}\times\dfrac{6}{7}\right):\left(4,2\times\dfrac{10}{11}+5\dfrac{2}{11}\right)\\ =\left(\dfrac{12}{7}-\dfrac{7}{6}\times\dfrac{6}{7}\right):\left(\dfrac{21}{5}\times\dfrac{10}{11}+\dfrac{57}{11}\right)\\ =\left(\dfrac{17}{7}-1\right):\left(\dfrac{42}{11}+\dfrac{57}{11}\right)\\ =\dfrac{10}{7}:9\\ =\dfrac{10}{63}\)

\(\left(6:\dfrac{3}{5}-1\dfrac{1}{6}\times\dfrac{6}{7}\right):\left(4,2\times\dfrac{10}{11}+5\dfrac{2}{11}\right)\)

\(=\left(6\times\dfrac{5}{3}-\dfrac{7}{6}\times\dfrac{6}{7}\right):\left(\dfrac{21}{5}\times\dfrac{10}{11}+\dfrac{57}{11}\right)\)

\(=\left(10-1\right):\left(\dfrac{42}{11}+\dfrac{57}{11}\right)=9:9=1\)

Một hình thang có hiệu hai đáy là 18 cm, đáy bé bằng 3/5 đáy lớn, đáy lớn bằng 3/2 chiều cao. Tình diện tích của hình thang đó ?

Hỡi các thiên tài toán học, hãy giải giúp mình bài toán này !

                                                                                Trân trọng cảm ơn !

\(3^2\left(x+4\right)-5^2=5\cdot2^2\\ 9\left(x+4\right)-25=20\\ 9\left(x+4\right)=20+25\\ 9\left(x+4\right)=45\\ x+4=45:9\\ x+4=5\\ x=5-4\\ x=1\)

x/y=3/4

=>x/3=y/4

=>x/15=y/20

y/z=5/7

=>y/5=z/7

=>y/20=z/28

=>x/15=y/20=z/28=(2x+3y-z)/(2*15+3*20-28)=186/62=3

=>x=45; y=60; z=84

f: =>35x-5=96-6x

=>41x=101

hay x=101/41

g: =>3(x-3)=90-5(1-2x)

=>3x-9=90-5+10x

=>3x-9=10x+85

=>-7x=94

hay x=-94/7

h.3x - 2/6 - 5 = 3 - 2(x + 7)/4

<=> 3x - 2 - 30/6 = 3 - 2(x + 7)/4

<=> 3x - 32/6 = 3 - 2x - 14/4

<=> 3x - 32/6 = -2x - 11/4

<=> 6x - 64/12 = -6x - 33/12

<=> 6x - 64 = -6x - 33 <=> 12x = 31 <=> x = 31/12

`a, (4x+5) : 3 -121:11=14`

`=> (4x+5) : 3 - 11=14`

`=> (4x+5) : 3 =14+11`

`=> (4x+5) : 3 = 25`

`=> 4x+5=25xx3`

`=>4x+5= 75`

`=> 4x=75-5`

`=>4x=70`

`=>x= 70/4`

`=>x= 35/2`

`b, 2+4+6+...+x=2450`

Số lượng của dãy là :

`(x-2)/2 + 1= (x-2)/2 +2/2= x/2`

Tổng số lượng là :

\(\dfrac{\left(x+2\right)\cdot\dfrac{x}{2}}{2}=\dfrac{\dfrac{x^2}{2}+\dfrac{2x}{2}}{2}=\dfrac{x\left(x+2\right)}{4}\)

\(\dfrac{x\left(x+2\right)}{4}=2450\)

\(\Rightarrow x\left(x+2\right)=2450\cdot4\\ \Rightarrow x\left(x+2\right)=9800\)

`=>x=98`

`c,` `1` nhân `32` sao?

`d, 2x+3x=1505`

`=> (2+3)x=1505`

`=> 5x=1505`

`=> x= 1505:5`

`=>x= 301`

a) \(\dfrac{13}{20}+\dfrac{3}{5}+x=\dfrac{5}{6}\)

\(\Rightarrow\dfrac{5}{4}+x=\dfrac{5}{6}\)

\(\Rightarrow x=\dfrac{5}{6}-\dfrac{5}{4}\)

\(\Rightarrow x=\dfrac{-5}{12}\)

b) \(x+\dfrac{1}{3}=\dfrac{2}{5}-\dfrac{-1}{3}\)

\(\Rightarrow x+\dfrac{1}{3}=\dfrac{11}{15}\)

\(\Rightarrow x=\dfrac{11}{15}-\dfrac{1}{3}\)

\(\Rightarrow x=\dfrac{2}{5}\)

c)\(\dfrac{-5}{8}-x=\dfrac{-3}{20}-\dfrac{-1}{6}\)

\(\dfrac{-5}{8}-x=\dfrac{1}{60}\)

\(\Rightarrow x=\dfrac{-5}{8}-\dfrac{1}{60}\)

\(\Rightarrow x=\dfrac{-77}{120}\)

d) \(\dfrac{3}{5}-x=\dfrac{1}{4}+\dfrac{7}{10}\)

\(\Rightarrow\dfrac{3}{5}-x=\dfrac{19}{20}\)

\(\Rightarrow x=\dfrac{3}{5}-\dfrac{19}{20}\)

\(\Rightarrow x=\dfrac{-7}{20}\)

e) \(\dfrac{-3}{7}-x=\dfrac{4}{5}+\dfrac{-2}{3}\)

\(\Rightarrow\dfrac{-3}{7}-x=\dfrac{2}{15}\)

\(\Rightarrow x=\dfrac{-3}{7}-\dfrac{2}{15}\)

\(\Rightarrow x=\dfrac{-59}{105}\)

g) \(\dfrac{-5}{6}-x=\dfrac{7}{12}+\dfrac{-1}{3}\)

\(\Rightarrow\dfrac{-5}{6}-x=\dfrac{1}{4}\)

\(\Rightarrow x=\dfrac{-5}{6}-\dfrac{1}{4}\)

\(\Rightarrow x=\dfrac{-13}{12}\)

\(8x-48+4x-12-14=-x+4\)

\(\Leftrightarrow12x-75=-x+4\Leftrightarrow13x=79\Leftrightarrow x=\dfrac{79}{13}\)

\(-7\left(8-x\right)-6\left(x+9\right)=20-x\Leftrightarrow-56+7x-6x-54=20-x\)

\(\Leftrightarrow2x=130\Leftrightarrow x=65\)

\(9x-63-80+60x=-7x+15\Leftrightarrow76x=158\Leftrightarrow x=\dfrac{79}{38}\)

\(-96-16x-60+30x=-40x-16\Leftrightarrow54x=140\Leftrightarrow x=\dfrac{70}{27}\)

\(17x-102-14x-28=4x-24-2x+4\Leftrightarrow x=110\)

KHO THE

\(A=\frac{\left[\left(25-1\right):1+1\right]\left(25+1\right)}{2}=325.\)

\(B=\frac{\left[\left(51-3\right):2+1\right]\left(51+3\right)}{2}=675\)

\(C=\frac{\left[\left(81-1\right):4+1\right]\left(81+1\right)}{2}=861\)