数学中的方程求解是指找出哪些值（可能是数、函数、集合）可以使一个方程成立，或是指出这様的解不存在。方程是二个用等号相连的数学表达式，表达式中有一个或多个未知数，未知数为自由变量，解方程就是要找出未知数要在什么情形下，才能使等式成立。更准确的说，方程求解不一定是要找出未知数的值，也有可能是将未知数以表达式来表示。方程的解是一组可以符合方程的未知数，也就是说若用方程的解来取代未知数，会使方程变为恒等式。

例如方程x + y = 2x – 1的解为x = y + 1，因为若将方程中x取代为y + 1，方程会变成恒等式(y + 1) + y = 2(y + 1) – 1。也可以将y视为未知数，解则为y = x – 1。也可以将x和y都视为未知数，此时会有许多组的解，像是(x, y) = (1, 0)或是(x, y) = (2, 1)等，所有满足(x, y) = (a + 1, a)的都是上述方程的解。

In mathematics, to solve an equation is to find what values (numbers, functions, sets, etc.) fulfill a condition stated in the form of an equation (two expressions related by equality). When searching a solution, one or more free variables are designated as unknowns. A solution is an assignment of expressions to the unknown variables that makes the equality in the equation true. In other words, a solution is an expression or a collection of expressions (one for each unknown) such that, when substituted for the unknowns, the equation becomes an identity. A problem of solving an equation may be numeric or symbolic. Solving an equation numerically means that only numbers represented explicitly as numerals (not as an expression involving variables), are admitted as solutions. Solving an equation symbolically means that expressions that may contain known variables or possibly also variables not in the original equation are admitted as solutions.