Bài 9:

Ta có: \(a-4+\sqrt{16-8a+a^2}\)

\(=a-4+\sqrt{\left(a-4\right)^2}\)

\(=a-4+a-4\)

=2a-8

a)\(\dfrac{x^2-3}{x^2+2x\sqrt{3}+3}=\dfrac{\left(x-\sqrt{3}\right)\left(x+\sqrt{3}\right)}{\left(x+\sqrt{3}\right)^2}=\dfrac{x-\sqrt{3}}{x+\sqrt{3}}\)

\(\dfrac{x^2-2x\sqrt{15}+15}{x^2-15}=\dfrac{\left(x-\sqrt{15}\right)^2}{\left(x-\sqrt{15}\right)\left(x+\sqrt{15}\right)}=\dfrac{x-\sqrt{15}}{x+\sqrt{15}}\)

\(\dfrac{4x^2-6}{4x^2-4x\sqrt{6}+6}=\dfrac{\left(2x-\sqrt{6}\right)\left(2x+\sqrt{6}\right)}{\left(2x-\sqrt{6}\right)^2}=\dfrac{2x+\sqrt{6}}{2x-\sqrt{6}}\)

b) \(\dfrac{a^2+2a\sqrt{8}+8}{a^2-8}=\dfrac{\left(a+\sqrt{8}\right)^2}{\left(a+\sqrt{8}\right)\left(a-\sqrt{8}\right)}=\dfrac{a+\sqrt{8}}{a-\sqrt{8}}\)

\(\dfrac{9x^2-15}{9x^2-6x\sqrt{15}+15}=\dfrac{\left(3x-\sqrt{15}\right)\left(3x+\sqrt{15}\right)}{\left(3x-\sqrt{15}\right)^2}=\dfrac{3x+\sqrt{15}}{3x-\sqrt{15}}\)

\(\dfrac{a^2-2a\sqrt{7}+7}{a^2-7}=\dfrac{\left(a-\sqrt{7}\right)^2}{\left(a-\sqrt{7}\right)\left(a+\sqrt{7}\right)}=\dfrac{a-\sqrt{7}}{a+\sqrt{7}}\)

ai giúp mình đi mọi người

1:

Khi x=36 thì \(A=\dfrac{6+4}{6-4}=\dfrac{10}{2}=5\)

2: \(B=\dfrac{3\sqrt{x}-12+16-2\sqrt{x}}{x-16}=\dfrac{\sqrt{x}+4}{x-16}=\dfrac{1}{\sqrt{x}-4}\)

3: A=B*|x-2|

=>|x-2|=A/B=căn x+4

=>x-2=căn x+4 hoặc x-2=-căn x-4

=>x-căn x-6=0 hoặc x+căn x+2=0

=>x=9

6.24:

\(A=\dfrac{-3}{11}-\dfrac{8}{11}+\dfrac{11}{8}-\dfrac{3}{8}=-1+1=0\)

6.23

a: \(=\dfrac{-5-7}{3}=\dfrac{-12}{3}=-4\)

b: \(=\dfrac{45-72}{54}=\dfrac{-27}{54}=-\dfrac{1}{2}\)

 B1a)2/3             b)-1/18

Bài khó lắmmm tr oiii

B = \(\dfrac{4}{7}\) = \(\dfrac{4.4}{7.4}\) = \(\dfrac{16}{28}\); I = \(\dfrac{6}{13}\) = \(\dfrac{6.\left(-2\right)}{13.\left(-2\right)}\) = \(\dfrac{-12}{-26}\)

N = \(\dfrac{-5}{13}\) = \(\dfrac{-5.3}{13.3}\) = \(\dfrac{-15}{39}\); T = \(\dfrac{7}{21}\) = \(\dfrac{7.4}{21.4}\) = \(\dfrac{28}{84}\)

U = \(\dfrac{4}{11}\) = \(\dfrac{4.5}{11.5}\) = \(\dfrac{20}{55}\);   O = \(\dfrac{5}{25}\) = \(\dfrac{5.3}{25.3}\) = \(\dfrac{15}{75}\)

H = \(\dfrac{1}{5}\) = \(\dfrac{1.11}{5.11}\) = \(\dfrac{11}{15}\);    A = \(\dfrac{5}{8}\) = \(\dfrac{5.5}{8.5}\) = \(\dfrac{25}{40}\)

G =  \(\dfrac{-3}{17}\) = \(\dfrac{-3.5}{17.5}\) = \(\dfrac{-15}{85}\); D = \(\dfrac{4}{16}\) = \(\dfrac{4.5}{16.5}\) = \(\dfrac{20}{80}\)

???

thế đề đau bn

ủa sao đăng hình lên ko đc thế này-.-?

??

=>x+1/2+x+1/6+...+x+1/90=99,9

=>\(\left(x+x+...+x\right)+\left(\dfrac{1}{2}+\dfrac{1}{6}+...+\dfrac{1}{90}\right)=99.9\)

=>\(9x+\left(1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+...+\dfrac{1}{9}-\dfrac{1}{10}\right)=99.9\)

=>9x+(1-0,1)=99,9

=>9x=99,9+0,1-1=100-1=99

=>x=11

4,5

4,5