Nonlinear equations are mathematical expressions where the relationship between variables is not a straight line when graphed. Unlike linear equations, which can be represented in the form y = mx + b, nonlinear equations can take various forms, such as quadratic equations y = ax² + bx + c or exponential functions y = a * b^x. These equations often involve powers, roots, or other operations that make their graphs curve or bend. Solving nonlinear equations can be more complex than solving linear ones, as they may have multiple solutions or none at all. Techniques such as graphing, substitution, or numerical methods are often used to find solutions. Nonlinear equations are commonly found in fields like physics, engineering, and economics, where they model real-world phenomena that do not follow a straight-line pattern.