làm giải nha

72x31+72x19+72x29+28x79  

= 72 . ( 31 + 19 + 29 ) + 28 x 79

= 72 . 79 + 28 x 79

= 79 x ( 72 + 28)

= 79 x 100

= 7900

7900

k4=2345 k5=3752

A = \(\dfrac{2}{5}\) + \(\dfrac{1}{15}\) + \(\dfrac{3}{10}\)

A = \(\dfrac{12}{30}\) + \(\dfrac{2}{30}\) + \(\dfrac{9}{30}\)

A = \(\dfrac{23}{30}\) 

B = \(\dfrac{1}{2}\) -  \(\dfrac{1}{8}\) - \(\dfrac{1}{26}\)

B = \(\dfrac{52}{104}\)- \(\dfrac{13}{104}\) - \(\dfrac{4}{104}\)

B = \(\dfrac{35}{104}\)

A.2/5 + 1/15 + 3/10                           B. 1/2 - 1/8 - 1/26

= 6/15 + 1/15 +3/10                           = 4/8 - 1/8 - 1/26

= 7/15 + 3/10                                     = 3/8 - 1/26

= 14/30 + 9/30                                   = 78/208 - 8/208

= 23/30                                               = 70/208

                                                           = 35/104

\(\left(8\dfrac{2}{5}+5\dfrac{3}{4}\right).\dfrac{1}{2}=\left(\dfrac{42}{5}+\dfrac{23}{4}\right).\dfrac{1}{2}=\left(\dfrac{168}{20}+\dfrac{115}{20}\right).\dfrac{1}{2}=\dfrac{283}{20}.\dfrac{1}{2}=\dfrac{283}{40}\)

(8\(\dfrac{2}{5}\) + 5\(\dfrac{3}{4}\) ) x \(\dfrac{1}{2}\)

=( \(\dfrac{42}{5}\) + \(\dfrac{23}{4}\)) x \(\dfrac{1}{2}\)

= (  \(\dfrac{168}{20}\) + \(\dfrac{115}{20}\)) x \(\dfrac{1}{2}\)

= \(\dfrac{283}{40}\)

\(A=2002\times2002=2002^2\)

\(B=2000\times2024=\left(2002-2\right)\left(2002+22\right)\)

\(=2002^2+22\times2002-2\times2002-2\times22\)

\(=2002^2+20\times2002-44>2002^2\)

\(\Rightarrow A< B\)

A=2002×2002=20022

$B=2000\times 2024=\left(2002-2\right)\left(2002+22\right)$

=2002^2+22\times2002-2\times2002-2\times22=20022+22×2002−2×2002−2×22

=2002^2+20\times2002-44>2002^2=20022+20×2002−44>20022

$\Rightarrow A<B$

\(8\dfrac{1}{9}\times1\dfrac{1}{7}=\dfrac{8\times9+1}{9}\times\dfrac{1\times7+1}{7}\)

\(=\dfrac{73}{9}\times\dfrac{8}{7}=\dfrac{584}{63}\)

8 1/9 . 1 1/7

=73/9 .8/7

= 584/63

\(2\times\left(x-\dfrac{1}{2}\right)^2-\dfrac{5}{4}=-\dfrac{3}{4}\)

\(2\times\left(x-\dfrac{1}{2}\right)^2=-\dfrac{3}{4}+\dfrac{5}{4}\)

\(2\times\left(x-\dfrac{1}{2}\right)^2=\dfrac{1}{2}\)

\(\left(x-\dfrac{1}{2}\right)^2=\dfrac{1}{2}\div2\)

\(\left(x-\dfrac{1}{2}\right)^2=\dfrac{1}{2}\times\dfrac{1}{2}\)

\(\left(x-\dfrac{1}{2}\right)^2=\dfrac{1}{4}\)

\(\left(x-\dfrac{1}{2}\right)^2=\left(\dfrac{1}{2}\right)^2\)

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

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

\(x=1\)

2x(X-1/2)^2-5/4=-3/4

= 2 x ( X - 1/2 ) ^2 = -3/4 + 5/4

= 2x(X-1/2)^2 = 1/2

= (X-1/2)^2  = 1/2 : 2

= (X-1/2)^2 = 1/4

= (X-1/2)^2  = (1/2 )^2

= X - 1/2 = 1/2

= X = 1/2 + 1/2

= X = 1 

a) ( 3/5 + 1/4 ) - ( 3/2 - 7/5 )

= 17/20 - 1/10

= 3/4 

b) ( 3 - 5/3 ) - ( 2 - 7/5 ) 

= 4/3 - 3/5

= 11/15 

A = ( 1 + 1/2 ) x ( 1+ 1/3 ) x ( 1+ 1/4 ) x ( 1+ 1/5 ) x ( 1 + 1/6 ) 

= 3/2 x 4/3 x 5/4 x 6/5 x 7/6

= 7/2

( Các bạn giải nhanh giúp mình nha )

\(B=\dfrac{1}{1\times2}+\dfrac{1}{2\times3}+\dfrac{1}{3\times4}+...+\dfrac{1}{2009\times2010}\\ =\dfrac{1}{1}-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+...+\dfrac{1}{2009}-\dfrac{1}{2012}\\ =1-\dfrac{1}{2010}=\dfrac{2009}{2010}\)

Sửa đề :

\(B=\dfrac{1}{1.2}+\dfrac{1}{2.3}+\dfrac{1}{3.4}+...+\dfrac{1}{2009.2010}\)

\(B=\dfrac{1}{1}-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+...+\dfrac{1}{2009}-\dfrac{1}{2010}\)

\(B=\dfrac{1}{1}-\dfrac{1}{2010}\)

\(B=\dfrac{2009}{2010}\)