=(2,75-2,25)-0.6=0,5-0,6=-0,1

\(a,\dfrac{2}{3}.\dfrac{5}{4}-\dfrac{3}{4}.\dfrac{2}{3}=\dfrac{2}{3}.\left(\dfrac{5}{4}-\dfrac{3}{4}\right)=\dfrac{2}{3}.\dfrac{2}{4}=\dfrac{1}{3}\)

\(b,2.\left(\dfrac{-3}{2}\right)-\dfrac{7}{2}=-6.\dfrac{1}{2}-7.\dfrac{1}{2}=\left(-6-7\right).\dfrac{1}{2}=-13.\dfrac{1}{2}=\dfrac{-13}{2}\)

\(c,-\dfrac{3}{4}.5\dfrac{3}{13}-0,75.\dfrac{36}{13}=-\dfrac{3}{4}.\left(\dfrac{68}{13}-\dfrac{36}{13}\right)=-\dfrac{3}{4}.\dfrac{32}{13}=-\dfrac{24}{13}\)

a) \(\dfrac{2}{3}.\dfrac{5}{4}-\dfrac{3}{4}.\dfrac{2}{3}\)

\(=\dfrac{2}{3}.\left(\dfrac{5}{4}-\dfrac{3}{4}\right)\)

\(=\dfrac{2}{3}.\dfrac{2}{4}\)

\(=\dfrac{2}{3}.\dfrac{1}{2}\)

\(=\dfrac{1}{3}\)

b) \(2.\left(\dfrac{-3}{2}\right)^2-\dfrac{7}{2}\)

\(=2.\dfrac{9}{4}-\dfrac{7}{2}\)

\(=\dfrac{9}{2}-\dfrac{7}{2}\)

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

c) \(-\dfrac{3}{4}.5\dfrac{3}{13}-0,75.\dfrac{36}{13}\)

\(=-\dfrac{3}{4}.\dfrac{68}{13}-\dfrac{3}{4}.\dfrac{36}{13}\)

\(=\dfrac{3}{4}.\dfrac{-68}{13}-\dfrac{3}{4}.\dfrac{36}{13}\)

\(=\dfrac{3}{4}.\left(\dfrac{-68}{13}-\dfrac{36}{13}\right)\)

\(=\dfrac{3}{4}.\dfrac{-104}{13}\)

\(=\dfrac{3}{4}.\left(-8\right)\)

\(=-6\)

TL

B = -7x² + 9

-7x²  \(\le\)   0 \(\forall\)x

\(\Rightarrow\)B = -7x² + 9 \(\le\)9 \(\forall\) x

dấu "=" xảy ra \(\Leftrightarrow\) -7x²=0

                       \(\Leftrightarrow\) x=0

vậy..........

C = 2 - ( 3x - 4 )^4

ta có   ( 3x - 4 )^4  \(\ge\)  0  \(\forall\)x

\(\Rightarrow\)  C = 2 - ( 3x - 4 )^4  \(\le\) 2  \(\forall\) x

 dấu "=" xảy ra \(\Leftrightarrow\)  ( 3x - 4 )^4 =0

                        \(\Leftrightarrow\) 3x-4=0

                        \(\Leftrightarrow\)x=4/3

x=4/3 nha anh

HT

@@@@@@@@@@@@@

Ngon thí

mấy bài này 2 phần đầu ko tính hợp lí đc

a) \(=10\frac{1}{4}\cdot\frac{-5}{3}-8\frac{1}{4}\cdot\frac{-5}{3}-5=\left(10\frac{1}{4}-8\frac{1}{4}\right)\cdot\frac{-5}{3}-5\)

\(=\left(\frac{41}{4}-\frac{33}{4}\right)\cdot\frac{-5}{3}-5=2\cdot\frac{-5}{3}-5\)\(=\frac{-10}{3}-\frac{15}{3}=\frac{-25}{3}\)

b)\(=\frac{5}{7}+1+\frac{2}{7}+\frac{2^{10}\cdot\left(2^3\right)^3}{\left(2^2\right)^9}\)

\(=\frac{5}{7}+\frac{2}{7}+1+\frac{2^{10}\cdot2^9}{2^{27}}\)

\(=1+1+\frac{1}{2^8}=2+\frac{1}{256}=\frac{512}{256}+\frac{1}{256}=\frac{513}{256}\)

\(\frac{-3}{5}.\frac{1}{7}+0,6.\frac{-2}{7}+\frac{3}{5}.\frac{-4}{7}\)

\(=\frac{-3}{5}.\frac{1}{7}+-1,2.\frac{1}{7}+\frac{-12}{5}.\frac{1}{7}\)

\(=\left(\frac{-3}{5}+-1,2+\frac{-12}{5}\right).\frac{1}{7}\)

\(=\frac{-21}{5}.\frac{1}{7}=\frac{-3}{5}\)

\(\frac{-17}{18}.\left(1-\frac{1}{3}\right)-\frac{7}{18}.\frac{2}{3}+\left(-2\frac{2}{3}\right)\)

\(=\frac{-17}{18}.\frac{2}{3}-\frac{7}{18}.\frac{2}{3}-2-\frac{2}{3}\)

\(=\left(\frac{-17}{18}-\frac{7}{18}-1\right)-2\)

\(=-2\frac{1}{3}-2=-4\frac{1}{3}\)