Răspuns:
D) 2
Explicație pas cu pas:
[tex]\sqrt{128}=\sqrt{2^{7} } =2^{3} \sqrt{2}=8\sqrt{2}[/tex]
[tex]\sqrt{72}=\sqrt{36*2}=6\sqrt{2}[/tex]
[tex]\sqrt{4y}=2\sqrt{y}[/tex]
[tex]\sqrt{4y} +\sqrt{72}=\sqrt{128} <=> 2\sqrt{y} +6\sqrt{2}=8\sqrt{2}[/tex]
[tex]=> 2\sqrt{y}=8\sqrt{2}-6\sqrt{2} =2\sqrt{2} <=> \sqrt{y}=\sqrt{2} => y=2[/tex]
