b)ta có Q=4

<=>\(\dfrac{\sqrt{a}+1}{\sqrt{a}}\) =4 <->\(\sqrt{a}+1=4.\sqrt{a}\)

<->\(\sqrt{a}+1=4\sqrt{a}\)

<->-3\(\sqrt{a}\) =1<=>\(\sqrt{a}\) =\(\dfrac{-1}{3}\) 

<-> a=1/9 

vậy ..........

a)Q=\(\dfrac{1}{\sqrt{a}+1}-\dfrac{1}{a+\sqrt{a}}:\dfrac{\sqrt{a}-1}{a+2\sqrt{a}+1}\left(a>0\right)\)

Q=\(\dfrac{1}{\sqrt{a}+1}-\dfrac{1}{\sqrt{a}\left(\sqrt{a}+1\right)}:\dfrac{\sqrt{a}-1}{\left(\sqrt{a}+1\right)^2}\)

Q= \(\dfrac{\sqrt{a}-1}{\sqrt{a}\left(\sqrt{a}+1\right)}.\dfrac{\left(\sqrt{a}+1\right)^2}{\sqrt{a}-1}\) =\(\dfrac{\sqrt{a}+1}{\sqrt{a}}\) 

vậy...

b. so sánh

\(\sqrt{17}-3\sqrt{32}+\sqrt{17}-3\sqrt{32}\)

=(\(\sqrt{17}+\sqrt{17}\) )+(-3\(\sqrt{32}-3\sqrt{32}\) )

=-6\(\sqrt{32}\) 

vậy ....

500-(5x+70)=\(5^2\).4

500-(5x+70)=25.4

500-(5x+70)=100

5x+70=500-100

5x+70=400

5x=400-70

5x=330

x=330:5

x=66

vậy.....

mênh mông :))