hoa mắt (@_@)

3/4-3/2+1/2:5/12-1/4

3/4-3/2+1/2.12/5-1/2

3/4-3/2+6/5-1/2

3/4-6/4+6/5-1/2

-3/4+6/5-1/2

-15/20+24/20-10/20

9/20-10/20

-1/20

 \(0,5.1\frac{1}{3}.75\%:\frac{2}{5}+\frac{3}{5}\)

\(=\frac{1}{2}.\frac{4}{3}.\frac{3}{4}:\frac{2}{5}+\frac{3}{5}\)

\(=\frac{1}{2}.\frac{4}{3}.\frac{3}{4}.\frac{5}{2}+\frac{3}{5}\)

\(=\frac{5}{4}+\frac{3}{5}\)

\(=\frac{37}{20}\)

\(0,5.1\frac{1}{3}.75\%:\frac{2}{5}+\frac{3}{5}\)

\(=\frac{1}{2}.\frac{4}{3}.\frac{3}{4}:\frac{2}{5}+\frac{3}{5}\)

\(=\frac{1}{2}.\frac{4}{3}.\frac{3}{4}.\frac{5}{2}+\frac{3}{5}\)

\(=\frac{1.4.3.5}{2.3.4.2}+\frac{3}{5}\)

\(=\frac{5}{4}+\frac{3}{5}\)

\(=\frac{37}{20}\)

~Học tốt~

a)=-7/21+8/24

=-1/3+1/3

=0

b)=-3/5.(2/7+5/7)+23/5

=-3/5.7/7+23/5

=-3/5.1+23/5

=-3/5+23/5

=20/5=4

c)=75/100-11/2+5/10:5/12+1/4

=3/4-11/2+1/2:5/12+1/4

=3/4+-11/2+1/2.12/5+1/4

=3/4+-22/4+6/5+1/4

=-19/4+6/5+1/4

=(-19/4+1/4)+6/5

=-18/4+6/5

=-9/2+6/5

=-45/10+12/10

=-23/10

Tìm \(x\) câu a:

\(\frac13.x\) + \(\frac25.\left(x+1\right)\) = 0

\(\frac{5}{15}x\) + \(\frac{6}{15}x\) + \(\frac25\) = 0

\(\frac{11}{15}x\) = - \(\frac25\)

\(x=-\frac25:\frac{11}{15}\)

\(x\) = - \(\frac25\times\frac{15}{11}\)

\(x\) = - \(\frac{6}{11}\)

Vậy \(x=-\frac{6}{11}\)

Tìm \(x\) câu b:

\(x\) x 25% = 0,5

\(x\times0,25\) = 0,5

\(x=0,5:0,25\)

\(x=2\)

Vậy \(x=2\)

Câu 1a:

1/3x + 2/5(x + 1) = 0

1/3x + 2/5x + 2/5 = 0

1/3x + 2/5x = - 2/5

x(1/3 + 2/5) = -2/5

x.(5/15 + 6/15) = -2/5

x.11/15 = - 2/5

x = - 2/5 : 11/15

x = - 6/11

Vậy x = -6/11

Câu b:

x . 25%. x = 0,5

x.x = 0,5 : 25%

x^2 = 2

x = - \(\sqrt2\); x = \(\sqrt2\)

Vậy x ∈ {- \(\sqrt2\); \(\sqrt2\) )

Câu 1a:

1/3x + 2/5(x + 1) = 0

1/3x + 2/5x + 2/5 = 0

1/3x + 2/5x = - 2/5

x(1/3 + 2/5) = -2/5

x.(5/15 + 6/15) = -2/5

x.11/15 = - 2/5

x = - 2/5 : 11/15

x = - 6/11

Vậy x = -6/11

Câu b:

x . 25%. x = 0,5

x.x = 0,5 : 25%

x^2 = 2

x = - \(\sqrt2\); x = \(\sqrt2\)

Vậy x ∈ {- \(\sqrt2\); \(\sqrt2\) )

Ta có

\(\frac{1}{2^2}+\frac{1}{3^2}+\frac{1}{4^2}+....+\frac{1}{11^2}>\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{11.12}\)

Mà

\(\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{11.12}=\frac{3-2}{2.3}+\frac{4-3}{3.4}\frac{5-4}{4.5}+...+\frac{12-11}{11.12}\)

\(=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{11}-\frac{1}{12}=\frac{1}{2}-\frac{1}{12}=\frac{5}{12}\)

Nên \(\frac{1}{2^2}+\frac{1}{3^2}+\frac{1}{4^2}+...+\frac{1}{11^2}>\frac{5}{12}\)

1/2^2+1/3^2+1/4^2+....+1/11^2<1/(2.3)+1/(3.4)+1/(4.5)+.....+1/(11.12)

                                                =1/2-13+1/3-1/4+1/5+.....+1/11-1/12

                                                =1/2-1/12=5/12

VẬY A<5/12

ks cho mình nhé

\(75\%-1\frac{1}{2}+0,5:\frac{5}{12}\)

\(=\frac{3}{4}-\frac{3}{2}+\frac{1}{2}.\frac{12}{5}\)

\(=\frac{3}{4}-\frac{3}{2}+\frac{6}{5}\)

\(=\frac{15}{20}-\frac{30}{20}+\frac{24}{20}\)

\(=\frac{9}{20}\)

bt rùi nhưng ko chắc lắm