\(\Leftrightarrow2x\left(x+5\right)-3\left(x-2\right)=7x+1\)

\(\Leftrightarrow2x^2+10x-3x+6-7x-1=0\)

\(\Leftrightarrow2x^2+5=0\)(vô lý)

ĐKXĐ:\(\left\{{}\begin{matrix}x\ne2\\x\ne-5\end{matrix}\right.\)

\(\dfrac{2x}{x-2}-\dfrac{3}{x+5}=\dfrac{7x+1}{x^2+3x-10}\\ \Leftrightarrow\dfrac{2x\left(x+5\right)}{\left(x+5\right)\left(x-2\right)}-\dfrac{3\left(x-2\right)}{\left(x+5\right)\left(x-2\right)}=\dfrac{7x+1}{x^2-2x+5x-10}\\ \Leftrightarrow\dfrac{2x^2+10x}{\left(x+5\right)\left(x-2\right)}-\dfrac{3x-6}{\left(x+5\right)\left(x-2\right)}=\dfrac{7x+1}{x\left(x-2\right)+5\left(x-2\right)}\\ \Leftrightarrow\dfrac{2x^2+10x}{\left(x+5\right)\left(x-2\right)}-\dfrac{3x-6}{\left(x+5\right)\left(x-2\right)}-\dfrac{7x+1}{\left(x+5\right)\left(x-2\right)}=0\)

\(\Leftrightarrow\dfrac{2x^2+10x-3x+6-7x-1}{\left(x+5\right)\left(x-2\right)}=0\\ \Leftrightarrow\dfrac{2x^2+5}{\left(x+5\right)\left(x-2\right)}=0\\ \Rightarrow2x^2+5=0\left(vô.lí\right)\)

Vậy pt vô nghiệm

5(3x + 8 ) - 7(2x + 3)     = 16

5.3x + 5.8 - (7.2x + 7.3) = 16

15x + 40 - 7.2x - 7.3      = 16

15x + 40 - 14x - 21        = 16

(15x - 14x) + (40 - 21)   = 16

15x - 14x + 19               = 16

15x - 14x                       = 16 - 19

x(15 - 14)                      = 16 - 19

x                                    = 16 - 19

x                                    = -3

A, \(2\frac{2}{5}\left(\frac{1}{2}x-0,75\right)=\frac{3}{10}\)

\(=>\frac{2.5+2}{5}\left(\frac{1}{2}x-\frac{3}{4}\right)=\frac{3}{10}\)

\(=>\frac{1}{2}x-\frac{3}{4}=\frac{3}{10}:\frac{12}{5}=\frac{1}{8}\)

\(=>x=\left(\frac{1}{8}+\frac{3}{4}\right):\frac{1}{2}\)

\(=>x=\frac{7}{4}\)

B, \(\frac{3}{5}-|x-\frac{1}{2}|=25\%\)

\(=>|x-\frac{1}{2}|=\frac{3}{5}-\frac{1}{4}\)

\(=>|x-\frac{1}{2}|=\frac{7}{20}\)

\(=>x-\frac{1}{2}=\frac{7}{20};-\frac{7}{20}\)

TH1: \(x-\frac{1}{2}=\frac{7}{20}=>x=\frac{17}{20}\)

TH2: \(x-\frac{1}{2}=-\frac{7}{20}=>x=\frac{3}{20}\)

a. \(\frac{1}{5}+\frac{3}{4}+\frac{1}{10}\)

= \(\frac{4}{20}+\frac{15}{20}+\frac{2}{20}\)

= \(\frac{21}{20}\)

b. \(\frac{5}{6}-\frac{1}{3}+\frac{1}{6}\)

= \(\frac{5}{6}-\frac{2}{6}+\frac{1}{6}\)

= \(\frac{4}{6}=\frac{2}{3}\)

c. \(\frac{3}{8}-\frac{10}{2}:\frac{4}{5}\)

= \(\frac{3}{8}-\frac{50}{8}\)

= \(\frac{-47}{8}\)

a) \(\frac{1}{5}+\frac{3}{4}+\frac{1}{10}\)

 = \(\frac{4+15+2}{20}\)

 = \(\frac{21}{20}\)

b) \(\frac{5}{6}-\frac{1}{3}+\frac{1}{6}\)

 = \(\frac{5-2+1}{6}\)

 = \(\frac{4}{6}\)

c) \(\frac{3}{8}-\frac{10}{2}:\frac{4}{5}\)

 = \(\frac{3}{8}-\frac{25}{4}\)

 = \(-\frac{47}{8}\)

b,1/5+3/4+1/10

=4/20+15/20+2/20

=21/20

a,5/6-1/3+5/6

5/6-2/6+5/6

=8/6

=4/3

c,3/8-10/2:4/5

=3/8-25/3

-191/24

nhớ k nha

2+6+12+20+...+90

Cách tính mk ko rành lắm xin các anh chị giúp đỡ 

đáp án là : 330

t nha

A = 1 x 2 + 2 x 3 + 3 x 4 + 4 x 5 + ... + 9 x 10

A x 3 = 1 x 2 x 3 + 2 x 3 x 3 + 3 x 4 x 3  + ... + 9 x 10 x 3

A x 3 = 1 x 2 x 3 + 2 x 3 x ( 4 - 1 ) + 3 x 4 ( 5 - 2 ) + ... + 9 x 10 x ( 11 - 8 )

A x 3 = 1 x 2 x 3 + 2 x 3 x 4 - 1 x 2 x 3 + 3 x 4 x 5 - 2 x 3 x 4 + 4 x 5 x 6 - 3 x 4 x 5 + ... + 9 x 10 x 11 - 8 x 9 x 10

A x 3 = 9 x 10 x 11

A = 9 x 10 x 11 : 3

A = 330

  Vậy A = 330

Đặt A = 1.2 + 2.3 + 3.4 + 4.5 + ... + 9.10

=> 3A = = 1.2.3 + 2.3.( 4 - 1 ) + 3.4. ( 5 - 2 ) + ... + 9.10.( 11 - 8 )

=> 3A = 1.2.3 - 1.2.3 + 2.3.4 - 2.3.4 + 3.4.5 - 3.4.5 + ...... + 8.9.10 - 9.10.11

=> 3A = 9.10.11

=> A = 9.10.11 : 3

Vậy A = 330

  Vậy A = 330

Đặt S=

1 x 2 + 2 x 3 + 3 x 4 + 4 x 5 + ............. + 9 x 10 

=>3S + 1.2.3+2.3.3+...+99.100.3

=>1.2.3+2.3(4-1)+3.4(5-2)+...+99.100(101-98)

=>1.2.3+2.3.4-1.2.3+3.4.5+-2.3.4+...+99.100.101-98.100.101

=>99.100.101=999900

=>S=333300

Lấy P(x) - Q(x) -2x^2 thì ra G(x) nhé 

Thanks bạn