Question

If x=3, then find the value of the expression $2{x^2} - 3x - 4$.

Answer 1

Hint: Here, we are given a quadratic expression with variable x and we need to find what will be the value of this expression when we put the value of x equal to 3. So, for finding this value, we just need to substitute the value of x with 3 in the given expression and solve the equation.

Complete step-by-step solution:
In this question, we are given a quadratic expression with variable x and we need to find the value of this quadratic expression when the value of x is equal to 3.
The given expression is : $2{x^2} - 3x - 4$ - - - - - - - - - - - - - (1)
Here, the variable is x.
A variable means the term that is not constant and can vary or change with time.
Here, we are given the value of this variable and we need to substitute that value in the given expression and find the value of the expression.
Therefore, on substituting x equal to 3 in the given expression, we get
$ \Rightarrow 2{x^2} - 3x - 4 = 2{\left( 3 \right)^2} - 3\left( 3 \right) - 4$
                             $
   = 2\left( 9 \right) - 9 - 4 \\
   = 18 - 9 - 4 \\
   = 9 - 4 \\
   = 5 \\
 $
Hence, the value of $2{x^2} - 3x - 4$ at x=3 is equal to 5.

Note: Here, note that there is no limit for the value of x. There can be an infinite number of values for x. On the other hand, if we were given that this expression is equal to 0, then the number of values for x would have been equal to 2 as the given expression is a quadratic equation.