1,
a,
=> $\sqrt{x^2+2x+1}$ =7
=> $\sqrt{(x+1)^2}$ = 7
=> x+1 =7
=> x=7-1 =6
b,
⇒ $\sqrt{x^2}$- 3 $\sqrt{x}$ =0
=>$\sqrt{x}$ ($\sqrt{x}$ -3 ) =0
=>\(\left[ \begin{array}{l}\sqrt{x=0}\\\sqrt{x}-3=0\end{array} \right.\)
=>\(\left[ \begin{array}{l}x=0\\x=9\end{array} \right.\)