91Ó°ÊÓ

• To get rid of a number in addition from one side, subtract the same number from both sides of the equal sign.
• To get rid of a number in subtraction from one side, add the same number on both sides of the equal sign.
• To get rid of a number in multiplication from one side, divide the same number from both sides of the equal sign.
• To get rid of a number in the division from one side, multiply the same number on both sides of the equal sign.

Rules of Addition/ Subtraction:

• Two numbers with similar signs 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 the larger number.

Rules of Multiplication/ Division:

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

In order to calculate $3a^2−2ab+c$, substitute $-3$for $a,-2$for $b$, and 3 for $c$.

$3a^2−2ab+c=3{\left(−3\right)}^2−2\left(−3\right)\left(−2\right)+3$

Further, simplify the expression by applying the rules of BODMAS.

$3a^2−2ab+c=3{\left(−3\right)}^2−2\left(−3\right)\left(−2\right)+3$

$$\begin{gathered} =3×9−2×6+3 \\ =27−12+3 \\ =15+3 \\ =18 \end{gathered}$$