theory of equation in math?

Answer 1

What's the question?

Answer 2

An equation is a mathematical statement, in symbols, that two things are the same (or equivalent). Equations are written with an equal sign, as in

2 + 3 = 5.
Equations are often used to state the equality of two expressions containing one or more variables. For example, given any value of x, it is always true that

x − x = 0.
The two equations above are examples of identities: equations that are true regardless of the values of any variables that appear within them. The following equation is not an identity:

x + 1 = 2.

Answer 3

Equation is an expression that agrees on a statement.

For example: New York is in U.S.A is a close statement. i.e we can do nothing about it.
Similar way x+1=5 is an close statement (equation). Only one value will fit in it.

Equation should agree both left and right hand side.

for example: x+3=17 - x
solution of x+3 should agree with solution of 17-x.

One can write a whole book on this topic.

Answer 4

Well I don't understand your question really. But an equation is anything with an equal sign... something = something else