\(\left(a-\dfrac{a^2+b^2}{a+b}\right)\left(\dfrac{1}{b}+\dfrac{2}{a-b}\right)\)

\(=\dfrac{a^2+ab-a^2-b^2}{a+b}\cdot\dfrac{a-b+2b}{b\left(a-b\right)}\)

\(=\dfrac{b\left(a-b\right)}{a+b}\cdot\dfrac{a+b}{b\left(a-b\right)}\)

=1

a: ĐKXĐ: \(x\le0\)

b: ĐKXĐ: \(x\le2\)

\(a,ĐK:-3x\ge0\Leftrightarrow x\le0\left(-3< 0\right)\\ b,ĐK:4-2x\ge0\Leftrightarrow-2x\ge-4\Leftrightarrow x\le2\\ c,ĐK:\dfrac{1}{2x-5}\ge0\Leftrightarrow2x-5>0\left(1>0;2x-5\ne0\right)\\ \Leftrightarrow x>\dfrac{5}{2}\\ d,ĐK:\dfrac{4x+7}{-3}\ge0\Leftrightarrow4x+7\le0\left(-3< 0\right)\Leftrightarrow x\le-\dfrac{7}{4}\)

a: \(\sqrt{252}+\dfrac{1}{3}\sqrt{63}-\sqrt{175}\)

\(=4\sqrt{7}+\sqrt{7}-5\sqrt{7}\)

=0

\(A=\frac{5}{2.1}+\frac{4}{1.11}+\frac{3}{11.2}+\frac{1}{2.15}+\frac{13}{15.4}\)

\(=\frac{1}{7}\left(\frac{5}{2.7}+\frac{4}{7.11}+\frac{3}{11.14}+\frac{1}{14.15}+\frac{13}{15.28}\right)\)

\(=\frac{1}{7}\left(\frac{1}{2}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+\frac{1}{11}-\frac{1}{14}+\frac{1}{14}-\frac{1}{15}+\frac{1}{15}-\frac{1}{28}\right)\)

\(=\frac{1}{2}\left(\frac{1}{2}-\frac{1}{28}\right)\)

\(=\frac{1}{2}.\frac{13}{28}\)

\(=\frac{13}{56}\)

unpollute

deforestation

environmental

pollution

conservationists

prevention

extremely

environmentalist

protection

seriously

poisonous

txđ D=R

y'=-3x²+6x+3m 

y' là tam thức bậc 2 nên y'=0 có tối đa 2 nghiệm 

để hs nb/(0;\(+\infty\) ) thì y' \(\le\) 0 với mọi x \(\in\) (0;\(+\infty\) )

\(\Leftrightarrow\) -3x² +6x+3m \(\le\) 0 với mọi x \(\in\) (0;\(+\infty\) )

\(\Leftrightarrow\) m\(\le\) x² -2x với mọi x \(\in\) (0; \(+\infty\) ) 

xét hs g(x)=x² -2x

g'(X) =2x-2

g'(x)=0 \(\Leftrightarrow\) x=1

 vậy m \(\le\) -1 

an unforgetable (không thể quên được)