cái này trong SGK thì tra google thì nhanh hơn đó bạn *ý kiến riêng* 

Chúc bạn học tốt! :3

20C

1C 2D
1 phải là cook nhé, cooker là nồi cơm điện rồi

19B

a: AB/AC=5/6

=>HB/HC=25/36

=>HB/25=HC/36=k

=>HB=25k; HC=36k

AH^2=HB*HC

=>25k*36k=30^2

=>900k^2=900

=>k=1

=>x=25cm; y=25cm

b: AB/AC=3/4

=>HB/HC=9/16

=>x/y=9/16

=>x/9=y/16=(x+y)/(9+16)=125/25=5

=>x=45cm; y=80cm

b.

\(\lim\limits_{x\rightarrow-\infty}\left(\sqrt{x^2+3x-1}+x\right)=\lim\limits_{x\rightarrow-\infty}\left(\dfrac{3x-1}{\sqrt{x^2+3x-1}-x}\right)\)

\(=\lim\limits_{x\rightarrow-\infty}\left(\dfrac{3-\dfrac{1}{x}}{-\sqrt{1+\dfrac{3}{x}-\dfrac{1}{x^2}}-1}\right)=\dfrac{3-0}{-1-1}=-\dfrac{3}{2}\)

d.

\(\lim\limits_{x\rightarrow-\infty}\dfrac{2x^2+3x}{\sqrt{4x^4+2x^2}+3x^2-1}=\lim\limits_{x\rightarrow-\infty}\dfrac{2+\dfrac{3}{x}}{\sqrt{4+\dfrac{2}{x^2}}+3-\dfrac{1}{x^2}}\)

\(=\dfrac{2+0}{\sqrt{4+0}+3-0}=\dfrac{2}{5}\)

7:

a: \(P=\left(1:\dfrac{x-x+1}{\sqrt{x}+\sqrt{x-1}}-\dfrac{x-1-2}{\sqrt{x-1}-\sqrt{2}}\right)\cdot\left(\dfrac{2\sqrt{x}-\sqrt{x}-\sqrt{2}}{\sqrt{x}\left(\sqrt{2}-\sqrt{x}\right)}\right)\)\(=\left(\sqrt{x}+\sqrt{x-1}-\sqrt{x-1}-\sqrt{2}\right)\cdot\dfrac{\sqrt{x}-\sqrt{2}}{\sqrt{x}\left(\sqrt{2}-\sqrt{x}\right)}\)

\(=-\dfrac{\left(\sqrt{x}-\sqrt{2}\right)}{\sqrt{x}}\)

b: Khi x=3-2căn 2 thì \(P=-\dfrac{\sqrt{2}-1-\sqrt{2}}{\sqrt{2}-1}=\dfrac{1}{\sqrt{2}-1}=\sqrt{2}+1\)

B

D

Hình như có sai sai thật

đáp án ra số lẻ đó pn, kq này nèk: \(\frac{313}{124}\)

D