Question

If $x - 4 = 5$, then what is the value of $x$ ?
A. $ - 1$
B. $9$
C. $ - 9$
D. $1$

Answer 1

Hint: The given equation we have to find the value of the required term. They give the relation for the required terms. By using the relation, we are going to find the value of $x$ substituting that in a simple algebraic expression in one variable. Then solve it by shifting the numeric term on the LHS to RHS.

Complete step-by-step answer:
 We are given an algebraic expression here. Before solving this little algebraic expression, let’s understand what actually is an algebraic expression.
In mathematical terms, an algebraic expression is an expression which consists of variables and constants, along with algebraic operations (addition, subtraction, multiplication and division).
Algebraic expressions can either have one variable, two variables or more.
For example:
1) $3x + 8y = 10$ is an expression in two variables. These types of expressions can be solved by certain methods like substitution, elimination and cross multiplication.
2)$3{x^2} - 4xy = 25$ is another expression in two variables.
3) $4x - 8 = 20$ is an expression in one variable. This is the simplest to solve. We just have to shift the terms so that the like terms are on one side and in this way, answers can be found.
Now, let’s solve the given simple algebraic expression.
$ \Rightarrow x - 4 = 5$
By observation, we know that this equation is in one variable and it can be solved by simply shifting the constant term on the LHS to RHS. Hence, simplifying-
$ \Rightarrow x = 5 + 4$
$ \Rightarrow x = 9$

Hence, our answer is option (B)

Note: The students must be aware of the fact that when we shift the terms on the other side, the sign of term changes. For example: In the given equation $x - 4 = 5$, when $4$ is on the LHS it has a negative sign. But when we shift it to the RHS, the sign changes to the positive sign. $ \Rightarrow x = 4 + 5$