$\dfrac{2+\sqrt{2}}{\sqrt{2}+1}+\dfrac{2-\sqrt{2}}{\sqrt{2}-1}-\sqrt{18}\\=\dfrac{(2+\sqrt{2})(\sqrt{2}-1)}{(\sqrt{2}-1)(\sqrt{2}+1)}+\dfrac{(2-\sqrt{2})(\sqrt{2}+1)}{(\sqrt{2}-1)(\sqrt{2}+1)}-3\sqrt{2}\\=\dfrac{2\sqrt{2}+2-2-\sqrt{2}}{2-1}+\dfrac{2\sqrt{2}-2+2-\sqrt{2}}{2-1}-3\sqrt{2}\\=2\sqrt{2}-\sqrt{2}+2\sqrt{2}-\sqrt{2}-3\sqrt{2}\\=-\sqrt{2}$

`a)P(x)=x^5 -3x-(7x-x^2+2x^3)+2x`

`=x^5 -3x-7x+x^2 -2x^3 +2x`

`=x^5 -2x^3 +x^2 +(-3x-7x+2x)`

`=x^5 -2x^3 +x^2-8x`

`Q(x)=8-x^5 +3-2(x^3 +6x)+11x^2+8x`

`=-x^5 -2x^3 +11x^2 -12x+8x+8`

`=-x^5 -2x^3 +11x^2 -4x+8`

Đáp án: `bbD`

Giải:

`P=(2x+2019)/(2(3x-1)-3(x-1))`

`=(2x+2019)/(6x-2-3x+3)`

`=(2x+2019)/(3x+1)`

ĐKXĐ:`3x+1\ne0`

`<=>3x\ne-1`

`<=>x\ne-1/3`

`3/5:x=2/3+4`

`3/5:x=14/3`

`x=3/5:14/3`

`x=9/70`

`42xx x=708+846`

`42xx x= 1554`

`x=1554:42`

`x=37`

$P=(\dfrac{\sqrt{x}}{2}-\dfrac{1}{2\sqrt{a}})(\dfrac{\sqrt{a}-1}{\sqrt{a}+1}-\dfrac{\sqrt{a}+1}{\sqrt{a}-1}\\=\dfrac{\sqrt{a}\sqrt{a}-1}{2\sqrt{a}}.\dfrac{(\sqrt{a}-1)(\sqrt{a}-1)-(\sqrt{a}+1)(\sqrt{a}+1)}{(\sqrt{a}+1)(\sqrt{a}-1)}\\=\dfrac{a-1}{2\sqrt{a}}.\dfrac{a-2\sqrt{a}+1-a-2\sqrt{a}-1}{a-1}\\=\dfrac{-4\sqrt{a}}{2\sqrt{a}}\\=-2$

thiếu `1` câu còn cọu :=:?

`3` câu mà?

$15.4\\=3.5.4\\=3.20\\=60\\25.12\\=25.4.3\\=100.3\\=300\\125.16\\=125.8.2\\=1000.2\\=2000$

:D