1.
![2x^3 - (1)/(x) =2x^3 - x^(-1)](https://img.qammunity.org/2019/formulas/mathematics/high-school/6s3nyppijs7r3taua57c7riccwcps52sk0.png)
is not a polynomial, because the degree of second term is negative (-1);
2.
![x^3y - 3x^2 + 6x](https://img.qammunity.org/2019/formulas/mathematics/high-school/jy93n2qin0c8yw8f6742uy2vsdccb5vzbi.png)
is a polynomial of 4th degree (the highest degree of all terms is 3+1=4);
3.
![y^2 + 5y - √(3)](https://img.qammunity.org/2019/formulas/mathematics/high-school/k925za3uq9dnjd5f8wzgmvtkolz7lmzj9q.png)
is a polynomial of 2th degree (the highest degree of all terms is 2);
4.
![2- √(4x) =2-1x^{ (1)/(2) }](https://img.qammunity.org/2019/formulas/mathematics/high-school/oxc0rnh3vyo4vpklqrq9ilkm78l6wem5vk.png)
is not a polynomial, because the degree of second term is a fraction
![(1)/(2)](https://img.qammunity.org/2019/formulas/mathematics/college/q5zg49mbtfrwobmmahi676fbgez56hhab0.png)
;
5.
![-x √(6)](https://img.qammunity.org/2019/formulas/mathematics/high-school/k7pv8qinpfk38u0izsqsuo1ht9xaqc7lxr.png)
is a monomial with 1st degree;
6.
![-(1/3)^(x^3) - (1/2)^(x^2)+ 1/4](https://img.qammunity.org/2019/formulas/mathematics/high-school/b703e0hyftg6v0l25byzfxm1llugwqzchv.png)
is not a polynomial, because here the variable x is placed in degree.