a,√4x²-4x+9=3
⇔(√4x²-4x+9)²=3²
⇔4x²-4x+9=9
⇔4x²-4x=0
⇔4x(x-1)=0
⇔\(\left[ \begin{array}{l}4x=0\\x-1=0\end{array} \right.\)
⇔\(\left[ \begin{array}{l}x=0\\x=1\end{array} \right.\)
b,$\left \{ {{3x-y=5} \atop {2y-x=0}} \right.$
⇔$\left \{ {{3x-y=5} \atop {x=2y}} \right.$
⇔$\left \{ {{3.2y-y=5} \atop {x=2y}} \right.$
⇔$\left \{ {{6y-y=5} \atop {x=2y}} \right.$
⇔$\left \{ {{5y=5} \atop {x=2y}} \right.$
⇔$\left \{ {{y=1} \atop {x=2}} \right.$
Vậy hpt có nghiệm (x;y)= (2;1)
