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\(\frac{5}{12}\cdot\frac{19}{6}+\frac{1}{6}-\frac{5}{12}\cdot\frac{7}{6}\)

\(=\frac{5}{12}\left(\frac{19}{6}-\frac{7}{6}\right)+\frac{1}{6}\)

\(=\frac{5}{12}\cdot\frac{19-7}{6}+\frac{1}{6}\)

\(=\frac{5}{12}\cdot\frac{12}{6}+\frac{1}{6}\)

\(=\frac{5\cdot12}{12\cdot6}+\frac{1}{6}\)

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

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

= 5/12*16/9+2/12-5/12*7/6

= 5/12*(19/6+1-7/6)

= 5/12*3

= 5/4

\(\left(3x+1\right)^2:\left(-\frac{1}{4}\right)=-\frac{49}{4}\)

\(\Leftrightarrow\left(3x+1\right)^2=-\frac{49}{4}\cdot\left(-\frac{1}{4}\right)\)

\(\Leftrightarrow\left(3x+1\right)^2=\frac{49}{16}\)

\(\Leftrightarrow\orbr{\begin{cases}\left(3x+1\right)^2=\left(\frac{7}{4}\right)^2\\\left(3x+1\right)^2=\left(-\frac{7}{4}\right)^2\end{cases}\Leftrightarrow\orbr{\begin{cases}3x+1=\frac{7}{4}\\3x+1=-\frac{7}{4}\end{cases}}}\)

\(\Leftrightarrow\orbr{\begin{cases}3x=\frac{3}{4}\\3x=-\frac{11}{4}\end{cases}\Leftrightarrow\orbr{\begin{cases}x=\frac{1}{4}\\x=-\frac{11}{12}\end{cases}}}\)

(3x+1)² =49/16

(=)3x+1=7/4

(=)3x=3/4

(=)x=1/4

Đề ko sai đâu

ta có A= 1+2+2²+2³+...+2²⁰¹⁸

=> 2A=2 +2²+2³+2⁴+....+2²⁰¹⁹

=> 2A-A=(2+2²+2³+2⁴+...+2²⁰¹⁹)-(1+2+2²+2³+....+2²⁰¹⁸)

=> A=2+2²+2³+3⁴+...+2²⁰¹⁹-1-2-2²-2³-...-2²⁰¹⁸

=> A= 2²⁰¹⁹-1

Vậy A=2²⁰¹⁹ -1

tk mk nha bn 

*****Chúc bạn học giỏi*****

Sai đề chăng ?

\(-\frac{3}{5}.\frac{11}{7}+\frac{3}{-5}.\frac{4}{7}+\frac{23}{7}\)

\(=\frac{-3}{5}\left(\frac{11}{7}+\frac{4}{7}\right)+\frac{23}{7}\)

\(=\frac{-3}{5}.\frac{15}{7}+\frac{23}{7}\)

\(=\frac{-9}{7}+\frac{23}{7}=2\)

a) (-25). ( 35-147) + 35. (25-147)

= -875  +  3675      + 875 -  5145

=    (  -875 + 875 ) + 3675 - 5145 

=           0                + ( - 1470 )

=                - 1475

thanks