There are some basic rules to follow to decide when to use a capital letter and when to leave the first letter lowercase. Actually, maybe I should state that many rules in English capitalization, do not apply in Spanish. In Spanish you do not capitalize the names of the days of the week, or the months of the year.
Equations and Expressions are closely related. The primary difference between the two is an equals sign. An equation has a left side, a right side and an equals sign separating the sides. An expression, by contrast, doesn't have any sides and is simply what the name suggests: An algebraic expression.. Though sometimes it is possible to combine like terms, we are generally not expected to do or solve anything regarding expressions.
Difference between identity and equation. An identity is true for any value of the variable, but an equation is not. For example the equation is true only when x=4, so it is an equation, but not an identity. In fact, when we see an equation like that, we are usually trying to solve it. That is, find the single value of x that makes the equation true.