What is the Function Relationship between X and Y?

[Vital]

Hello!
I have just joined this wonderful community. I do my best to learn math and other sciences on my own. Rather difficult thing to do, but I do hope to cope with this interesting task. I will be asking questions hoping to get help. :)
Thank you!
Best wishes!

 

[Greg Bernhardt]

Welcome to PF!

 

[Vital]

Welcome to PF!

Thank you very much! Wonderful site. Great work. :)

 

[liuhongwei]

你能帮助我吗 ？
问：以下哪个表达式表示y是X的函数？
①2y + x = 3; ②y = x + 2z; ③y = 2；④y = kx + 1（k为常数。）；⑤y²= x