Question

If $9x - 13 = - 31$, how do you find the value of $x - 8$ ?

Answer 1

Hint: The above problem is based on the basic mathematical calculations to find the value of variable given in the equation.
Variable value depends upon the equation and the operations we will perform to calculate the unknown value.
Using basic mathematical operations we will perform the calculation.

Complete step by step answer:
Let’s discuss mathematical operations to be done in order to calculate the given value of expression.
When an integer is shifted from RHS to LHS and LHS to RHS its sign changes, that is from positive to negative and negative to positive. When an equation contains a variable then we must separate the variable on one side and constant on one side. If the coefficient of variable is one then the value of the variable can be calculated directly, if the coefficient of variable is more than one, then that constant value must be divided with the other constant value which was separated.
Now, we will perform the calculations to calculate the value of x.
$ \Rightarrow 9x - 13 = - 31$ (Given equation)
$ \Rightarrow 9x = - 31 + 13$ (We have shifted the constant from LHS to RHS)
$ \Rightarrow 9x = - 18$
$ \Rightarrow x = \dfrac{{ - 18}}{9} = - 2$ (Performed the division and value of variable is calculated)
Now, we will substitute the value of x in x – 8
$ \Rightarrow - 2 - 8$ (x = -2 substituted)
$ \Rightarrow - 10$ (Final answer)

Note: The applications of the equations we were given in the question can be seen in simultaneous equations, of matrix to find out whether the given system of equations has unique, infinite or no solution, in solving network circuit problems where value of variable is calculated that is current or voltage.