Which expressions are polynomials?

there can be more than one answer.

For an expression to be a polynomial, exponents of variables must be a natural number (1, 2, 3, etc.) or 0. So exponents on variables cannot have negative exponents or roots (as roots are fraction exponents). As the third answer choice, 5x^2 - sqrt(x), contains the square root of a variable ( sqrt(x) is also equal to x^(1/2) ), it is not a polynomial.

If given the value of an angle of the right triangle (aside from the 90° angle), then the trigonometric ratios will be more useful for solving for the sides of the triangle. One could use sin, cosin, and tangeant, the main trigonmetric ratios to solve for all sides and angles of the triangle, if given at least one angle and one side length. 

The Pythagorean Theorem as it is generally applied, helps solve for the third side of a triangle, given that you know the other 2 sides. This is less applicable, and trigonometric ratios can also be used in this case to solve for the rest of the triangle's angles and the third side.