The Sort command on the Polynomials submenu collects numeric coefficients of terms of a polynomial expression and returns the terms in order of decreasing degree. The Collect command on the Polynomials submenu collects all coefficients of terms of a polynomial expression, but does not necessarily sort the terms by degree. Specify your choice of polynomial variable in the dialog box that appears.
Polynomials + Sort
5t2 +2t - 16t5 + t3 -2t2 +9 + at2 = -16t5 + t3 +3t2 + at2 + 2t + 9 (The variable is t.)
x2 +3x + 5 - 3x3 +5x2 +4x3 +13 + 2x4 = 2x4 + x3 +6x2 + 3x + 18
5t2 +3xt2 -16t5 + y3 -2xt2 +9 = t2x + 5t2 -16t5 + y3 + 9 (The variable is x.)
5t2 +3xt2 -16t5 + y3 -2xt2 +9 = -16t5 + xt2 +5t2 + y3 + 9 (The variable is t.)
Polynomials + Collect
5t2 +2t - 16t5 + t3 -2t2 +9 + at2 = -16t5 + t3 +3 + a
t2 + 2t + 9 (The variable is t.)
x2 +3x + 5 - 3x3 +5x2 +4x3 +13 + 2x4 = 6x2 +3x + 18 + x3 +2x4 (The variable is x.)
5t2 +3xt2 -16t5 + y3 -2xt2 +9 = 5t2 + xt2 -16t5 + y3 + 9 (The variable is x.)
5t2 +3xt2 -16t5 + y3 -2xt2 +9 = -16t5 +x + 5
t2 +9 + y3 (The variable is t.)
For some expressions, you may want to apply both commands.
Polynomials + Collect, Polynomials + Sort
(The variable is x)
Polynomials + Sort, Polynomials + Collect
(The variable is x)