Giải giùm mình câu này   

1) x = UC(36,24) và x 20.

2) x = UC(60, 84, 120) và x≥ 6

3) 91:x;26:x và 10<x<30.

6) x = BC(6,4) và 16 < x <50.

7) x = BC(18, 30, 75) và 0<x<1000.

8) x:10;x:15 và x <100

4) 70:x;84:x và x8.

9) x:20; x:35 và x<500

5) 150:x: 84:x ; 30:x và 0<x<16.

10) x:12; x:21, x:28 và 150≤x≤400

11) (x+21):7; (x+21):8; (x+21):9 vaø 200 <x<

500 

1: \(36=2^2\cdot3^2;24=2^3\cdot3\)

Do đó: ƯCLN(36;24)\(=2^2\cdot3=12\)

x∈ƯC(36;24)

=>x∈Ư(12)

mà x<20

nên x∈{1;-1;2;-2;3;-3;4;-4;6;-6;12;-12}

2: \(60=2^2\cdot3\cdot5;84=2^2\cdot3\cdot7;120=2^3\cdot3\cdot5\)

Do đó: ƯCLN(60;84;120)\(=2^2\cdot3=12\)

x∈ƯC(60;84;120)

=>x∈Ư(12)

mà x>=6

nên x∈{6;12}

3: \(91=13\cdot7;26=2\cdot13\)

Do đó: ƯCLN(91;26)=13

91⋮x và 26⋮x

=>x∈ƯC(91;26)

=>x∈Ư(13)

mà 10<x<30

nên x=13

6: \(6=2\cdot3;4=2^2\)

Do đó: BCNN(6;4)\(=2^2\cdot3=4\cdot3=12\)

x∈BC(6;4)

=>x∈B(12)

mà 16<x<50

nên x∈{24;36;48}

7: \(18=2\cdot3^2;30=2\cdot3\cdot5;75=3\cdot5^2\)

Do đó: BCNN(18;30;75)\(=2\cdot3^2\cdot5^2=2\cdot15^2=450\)

x∈BC(18;30;75)

=>x∈B(450)

mà 0<x<1000

nên x∈{450;900}

8: \(10=2\cdot5;15=3\cdot5\)

Do đó: BCNN(10;15)\(=2\cdot3\cdot5=30\)

x⋮10 và x⋮15

=>x∈BC(10;15)

=>x∈B(30)

mà x<100

nên x∈{0;30;60;90}

4:

\(70=2\cdot5\cdot7;84=2^2\cdot3\cdot7\)

Do đó: ƯCLN(70;84)\(=2\cdot7=14\)

70⋮x; 84⋮x

=>x∈ƯC(70;84)

=>x∈Ư(14)

mà x>8

nên x=14

9: \(20=2^2\cdot5;35=5\cdot7\)

Do đó: BCNN(20;35)\(=2^2\cdot5\cdot7=140\)

x⋮20 và x⋮35

=>x∈BC(20;35)

=>x∈B(140)

mà x<500

nên x∈{140;280;420}

5: \(150=2\cdot3\cdot5^2;84=2^2\cdot3\cdot7;30=2\cdot3\cdot5\)

Do đó: ƯCLN(150;84;30)\(=2\cdot3=6\)

150⋮x; 84⋮x; 30⋮x

=>x∈ƯC(150;84;30)

=>x∈Ư(6)

mà 0<x<16

nên x∈{1;2;3;6}

10: \(12=2^2\cdot3;21=3\cdot7;28=2^2\cdot7\)

Do đó: BCNN(12;21;28)\(=2^2\cdot3\cdot7=84\)

x⋮12; x⋮21; x⋮28

=>x∈BC(12;21;28)

=>x∈B(84)

mà 150<=x<=400

nên x∈{168;252;336}

11:

\(7=7;8=2^3;9=3^2\)

Do đó: BCNN(7;8;9)\(=7\cdot2^3\cdot3^2=504\)

x+21 ⋮7; x+21⋮8; x+21⋮9

=>x+21∈BC(7;8;9)

=>x+21∈B(504)

=>x+21∈{504;1008;...}

=>x∈{483;987;...}

mà 200<x<500

nên x=483

50) \(\sqrt{98-16\sqrt{3}}=4\sqrt{6}-\sqrt{2}\)

51) \(\sqrt{2-\sqrt{3}}=\dfrac{\sqrt{4-2\sqrt{3}}}{\sqrt{2}}=\dfrac{\sqrt{3}-1}{\sqrt{2}}=\dfrac{\sqrt{6}-\sqrt{2}}{2}\)

52) \(\sqrt{4+\sqrt{15}}=\dfrac{\sqrt{8+2\sqrt{15}}}{\sqrt{2}}=\dfrac{\sqrt{5}+\sqrt{3}}{\sqrt{2}}=\dfrac{\sqrt{10}+\sqrt{6}}{2}\)

53) \(\sqrt{5-\sqrt{21}}=\dfrac{\sqrt{10-2\sqrt{21}}}{\sqrt{2}}=\dfrac{\sqrt{14}-\sqrt{6}}{2}\)

54) \(\sqrt{6-\sqrt{35}}=\dfrac{\sqrt{12-2\sqrt{35}}}{\sqrt{2}}=\dfrac{\sqrt{14}-\sqrt{10}}{2}\)

55) \(\sqrt{2+\sqrt{3}}=\dfrac{\sqrt{4+2\sqrt{3}}}{\sqrt{2}}=\dfrac{\sqrt{6}+\sqrt{2}}{2}\)

56) \(\sqrt{4-\sqrt{15}}=\dfrac{\sqrt{8-2\sqrt{15}}}{\sqrt{2}}=\dfrac{\sqrt{10}-\sqrt{6}}{2}\)

Can bac 8

a; \(\dfrac{9}{27}\) + \(\dfrac{7}{-49}\)

= \(\dfrac{1}{3}\) - \(\dfrac{1}{7}\)

= \(\dfrac{7}{21}\) - \(\dfrac{3}{21}\)

= \(\dfrac{4}{21}\)

b; - \(\dfrac{12}{10}\) + \(\dfrac{-25}{30}\)

   =  - \(\dfrac{6}{5}\) - \(\dfrac{5}{6}\)

   = -\(\dfrac{36}{30}\) - \(\dfrac{25}{30}\)

  = \(\dfrac{-61}{30}\) 

c; \(\dfrac{-20}{35}\) + \(\dfrac{-16}{-24}\)

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

= - \(\dfrac{12}{21}\) + \(\dfrac{14}{21}\)

=  \(\dfrac{2}{21}\)

d; - \(\dfrac{21}{77}\) + \(\dfrac{10}{-35}\)

 = - \(\dfrac{3}{11}\) - \(\dfrac{2}{7}\)

 = - \(\dfrac{21}{77}\) -  \(\dfrac{22}{77}\)

= - \(\dfrac{43}{77}\)

b.

ĐKXĐ: \(x\ge-1\)

\(\sqrt{\left(x+1\right)\left(x+35\right)}-14\sqrt{x+35}+84-6\sqrt{x+1}=0\)

\(\Leftrightarrow\sqrt{x+1}\left(\sqrt{x+35}-14\right)-6\left(\sqrt{x+35}-14\right)=0\)

\(\Leftrightarrow\left(\sqrt{x+1}-6\right)\left(\sqrt{x+35}-14\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}\sqrt{x+1}=6\\\sqrt{x+35}=14\end{matrix}\right.\)

\(\Leftrightarrow...\)

a. ĐKXĐ: \(-1\le x\le1\)

Đặt \(\left\{{}\begin{matrix}\sqrt{x+1}=a\ge0\\\sqrt{1-x}=b\ge0\end{matrix}\right.\)

\(\Rightarrow a+2a^2=-b^2+b+3ab\)

\(\Leftrightarrow\left(2a^2-3ab+b^2\right)+a-b=0\)

\(\Leftrightarrow\left(a-b\right)\left(2a-b\right)+a-b=0\)

\(\Leftrightarrow\left(a-b\right)\left(2a-b+1\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}a=b\\2a+1=b\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}\sqrt{x+1}=\sqrt{1-x}\\2\sqrt{x+1}+1=\sqrt{1-x}\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=0\\4x+5+4\sqrt{x+1}=1-x\left(1\right)\end{matrix}\right.\)

(1) \(\Leftrightarrow4\sqrt{x+1}=-4-5x\) \(\left(x\le-\dfrac{4}{5}\right)\)

\(\Leftrightarrow16\left(x+1\right)=25x^2+40x+16\)

\(\Leftrightarrow25x^2+24x=0\Rightarrow\left[{}\begin{matrix}x=0\left(loại\right)\\x=-\dfrac{24}{25}\end{matrix}\right.\)

cái này tính cái gì thế

ko hiểu

M=1−31​+1−151​+1−351​+1−631​+...+1−99991​

\(� = \left(\right. 1 + 1 + 1 + . . . + 1 \left.\right) - \left(\right. \frac{1}{3} + \frac{1}{15} + \frac{1}{35} + \frac{1}{63} + . . . + \frac{1}{9999} \left.\right)\)

\(� = \left(\right. 1 + 1 + 1 + . . . + 1 \left.\right) - \left(\right. \frac{1}{1.3} + \frac{1}{3.5} + \frac{1}{5.7} + \frac{1}{7.9} + . . . + \frac{1}{99.101} \left.\right)\)(Có (99 - 1): 2+ 1 = 50 số 1)

\(� = 50 - \frac{1}{2} . \left(\right. \frac{2}{1.3} + \frac{2}{3.5} + \frac{2}{5.7} + \frac{2}{7.9} + . . . + \frac{2}{99.101} \left.\right)\)

\(� = 50 - \left(\right. 1 - \frac{1}{3} + \frac{1}{3} - \frac{1}{5} + \frac{1}{5} - \frac{1}{7} + \frac{1}{7} - \frac{1}{9} + . . . + \frac{1}{99} - \frac{1}{101} \left.\right)\)

\(� = 50 - \left(\right. 1 - \frac{1}{101} \left.\right) = 50 - \frac{100}{101} = \frac{5050 - 100}{101} = \frac{4950}{101}\)

a)-112

b: =-30-15-21

=-66

toán lớp 5

2 x X + 68 = 126

2 x X = 126 - 68

2 x X = 58

      x = 58 : 2

      x = 29

a: \(\left(5+\frac15-\frac29\right)-\left(2-\frac{1}{23}-\frac{3}{35}+\frac56\right)-\left(8+\frac27-\frac{1}{18}\right)\)

\(=5+\frac15-\frac29-2+\frac{1}{23}+\frac{3}{35}-\frac56-8-\frac27+\frac{1}{18}\)

\(=\left(5-2-8\right)+\left(\frac15+\frac{3}{35}-\frac27\right)+\left(-\frac29-\frac56+\frac{1}{18}\right)+\frac{1}{23}\)

\(=\left(-5\right)+\left(\frac{7}{35}+\frac{3}{35}-\frac{10}{35}\right)+\left(-\frac{4}{18}-\frac{15}{18}+\frac{1}{18}\right)+\frac{1}{23}\)

\(=-5+\left(-\frac{18}{18}\right)+\frac{1}{23}=-6+\frac{1}{23}=-\frac{138}{23}+\frac{1}{23}=-\frac{137}{23}\)

c: \(-\frac57-\left(-\frac{5}{67}\right)+\frac{13}{10}+\frac12+\left(-\frac16\right)+1\frac{3}{14}-\left(-\frac25\right)\)

\(=-\frac57+\frac{5}{67}+\frac{13}{10}+\frac12-\frac16+\frac{17}{14}+\frac25\)

\(=\left(-\frac57+\frac{17}{14}+\frac12\right)+\left(\frac{13}{10}+\frac25-\frac16\right)+\frac{5}{67}\)

\(=\left(-\frac{10}{14}+\frac{17}{14}+\frac12\right)+\left(\frac{13}{10}+\frac{4}{10}-\frac16\right)+\frac{5}{67}\)

\(=\left(\frac{7}{14}+\frac12\right)+\left(\frac{17}{10}-\frac16\right)+\frac{5}{67}=1+\frac{5}{67}+\frac{51}{30}-\frac{5}{30}\)

\(=\frac{72}{67}+\frac{46}{30}=\frac{72}{67}+\frac{23}{15}=\frac{2621}{1005}\)

d: \(\frac35:\left(-\frac{1}{15}-\frac16\right)+\frac35:\left(-\frac13-1\frac{1}{15}\right)\)

\(=\frac35:\left(-\frac{2}{30}-\frac{5}{30}\right)+\frac35:\left(-\frac{5}{15}-\frac{16}{15}\right)\)

\(=\frac35:\left(-\frac{7}{30}\right)+\frac35:\left(-\frac{21}{15}\right)\)

\(=\frac35\cdot\frac{-30}{7}+\frac35\cdot\frac{-5}{7}=\frac35\cdot\left(-\frac{30}{7}-\frac57\right)\)

\(=\frac35\cdot\left(-\frac{35}{7}\right)=\frac35\cdot\left(-5\right)=-3\)