TryGetPolyLinear​(AngouriMath.​Entity,​AngouriMath.​Entity.​Variable,​AngouriMath.​Entity@,​AngouriMath.​Entity@)

using System;
using AngouriMath;
using static AngouriMath.MathS.Utils;

Entity expr = "(x^2 + 2)(a + b + 2x) + x + sin(h)";
if (TryGetPolynomial(expr, "x", out var dict))
    foreach (var (pow, coef) in dict)
        Console.WriteLine($"Pow: {pow}. Coef: {coef}");
Console.WriteLine("------------------------");
Entity expr1 = "sin(x) + a";
if (TryGetPolynomial(expr1, "x", out var dict1))
    foreach (var (pow, coef) in dict1)
        Console.WriteLine($"Pow: {pow}. Coef: {coef}");
else
    Console.WriteLine("Failed to interpret as polynomial");
Console.WriteLine("------------------------");
Entity expr2 = "(x + a)(b + x) + a + 2 + x";
if (TryGetPolyQuadratic(expr2, "x", out var a, out var b, out var c))
    Console.WriteLine($"The expr is ({a}) * x^2 + ({b}) * x + ({c})");
Console.WriteLine("------------------------");
Entity expr3 = "(b + x) + a + 2 + x";
if (TryGetPolyLinear(expr3, "x", out var a1, out var b1))
    Console.WriteLine($"The expr is ({a1}) * x + ({b1})");

Pow: 2. Coef: 1 * 1 ^ 2 * a + 1 * 1 ^ 2 * b
Pow: 3. Coef: 1 * 1 ^ 2 * 2
Pow: 0. Coef: 2 * a + 2 * b + sin(h)
Pow: 1. Coef: 1 * 2 * 2 + 1
------------------------
Failed to interpret as polynomial
------------------------
The expr is (1 * 1 ^ 2) * x^2 + (1 * b + 1 * a + 1) * x + (a * b + a + 2)
------------------------
The expr is (1 + 1) * x + (b + a + 2)