Question

How do you multiply \[\left( {3x - 5} \right)\left( {3x + 5} \right)\]?

Answer 1

Hint: Here in this question, we have to find the product of 2 binomials. The binomial is one form of algebraic expression. So let us have 2 binomials which are different from one another and then we use the arithmetic operation that is multiplication and then we simplify to get the required solution.

Complete step-by-step solution:
The binomial concept will come under the topic of algebraic expressions. The algebraic expression is a combination of variables and constant. The alphabets are known as variables and the numerals are known as constants. In algebraic expression or equation, we have 3 types namely, monomial, binomial and polynomial.
A polynomial equation with two terms joined by the arithmetic operation + or – is called a binomial equation.
Now let us consider the two binomial and they are \[\left( {3x - 5} \right)\], and \[\left( {3x + 5} \right)\]
Now we have to multiply the binomials, to multiply the binomials we use multiplication. The multiplication is one of the arithmetic operations.
Now we multiply the above 2 binomials we get
\[\left( {3x - 5} \right) \cdot \left( {3x + 5} \right)\]
Here dot represents the multiplication. First, we multiply the first two terms of the above equation
\[ \Rightarrow 3x\left( {3x + 5} \right) - 5\left( {3x + 5} \right)\]
On multiplying we get
\[ \Rightarrow 9{x^2} + 15x - 15x - 25\]
On simplification we have
\[ \Rightarrow 9{x^2} - 25\]
Hence, we have multiplied the two binomial numbers and obtained the solution for the question
Therefore, we have \[\left( {3x - 5} \right)\left( {3x + 5} \right) = 9{x^2} - 25\]
We can also solve the given question by using the standard algebraic formula \[(a + b)(a - b) = {a^2} - {b^2}\]. Here \[a = 3x\] and \[b = 5\]. On substituting the values in the formula, we get
\[ \Rightarrow \,\left( {3x - 5} \right)\left( {3x + 5} \right) = {\left( {3x} \right)^2} - {5^2}\]
\[ \Rightarrow \,\left( {3x - 5} \right)\left( {3x + 5} \right) = 9{x^2} - 25\]
Hence we have multiplied and obtained the solution.

Thus the correct answer is $9{x^2} - 25$

Note: To multiply we use operation multiplication, multiplication of numbers is different from the multiplication of algebraic expression. In the algebraic expression it involves the both number that is constant and variables. Variables are also multiplied, if the variable is the same then the result will be in the form of an exponent.