Chapter SH, Problem 9SEWI

Solution

To simplify the expression $\left(-7\right)\left(-4\right)$ .

  $28$

Given:

The expression, $\left(-7\right)\left(-4\right)$ .

Concept Used:

Rules of Addition/ Subtraction:

• Two numbers with similar sign always get added and the resulting number will carry the similar sign.
• Two numbers with opposite signs always get subtracted and the resulting number will carry the sign of larger number.

Rules of Multiplication/ Division:

• The product/quotient of two similar sign numbers is always positive.
• The product/quotient of two numbers with opposite signs is always negative.

Calculation:

In order to simplify the given expression $\left(-7\right)\left(-4\right)$ , note that the sign of both numbers is same, so the product of the numbers will be positive. So, multiply the numbers and keep the positive sign with the final result as shown below

  $\begin{array}{c}\left(-7\right)\left(-4\right)=+\left(7\cdot 4\right)\\ =+28\\ =28\end{array}$

Thus, the simplified expression is $28$ .