# 7.1 Algebraic Formulae

7.1 Algebraic Formulae

7.1.1 Variables and Constant
1. A variable is a quantity without a fixed value.
2. A constant is a quantity with a fixed value.

7.1.2 Concept of Formulae
1. An algebraic formula is an equation which shows the relationship between several variables and/ or constant.
2. The subject of an algebraic formula is a linear variable expressed in terms of the other variables.

Example 1:

Solution:
$\begin{array}{l}y=\frac{2-3x}{x}\\ xy=2-3x\\ xy+3x=2\\ x\left(y+3\right)=2\\ x=\frac{2}{y+3}\end{array}$

Example 2:

Solution:
$\begin{array}{l}s=\frac{{p}^{2}-{q}^{2}}{2r}\\ 2rs={p}^{2}-{q}^{2}\\ {p}^{2}=2rs+{q}^{2}\\ p=\sqrt{2rs+{q}^{2}}\end{array}$