The figure on the right shows a square tile. if the length of each side is represented in an unknown x, then its perimeter can be represented by the algebraic expressoin 4x.
When the length of the tile is 8 cm (that is, x=8), the perimeter of the square tile = 4x =4(8) =32 cm.
When the length of the tile is 15 cm (that is, x=15), the perimeter of the square tile = 4x =4(15) =60 cm.
In an algebraic expression, the method of replacing unknowns by numbers is called substitution, and the result obtained is the value of the algebraic expression.
The perimeter and the area of some plane figures can be represented by algebraic expressions. For a rectangle of length x cm and width y cm, the
Perimeter = x+x+y+y
= 2(x+y) cm and
Area = xy cm2.
If we use variables P cm and A cm 2 to represent the perimeter and the area, respectively, we have the following formulas:
P = 2(x+y) and A = xy
Once the values of x and y are known, we can find the corresponding unknown values of P and A from the formula by substitution. For example, if x = 4 cm and y = 3 cm, then
P = 2(x+y) and A = xy
=2(4+3) =4x3
=2(7) =12 cm2
=14 cm
The perimeter and area of the rectangle are 14 cm and 12 cm2, respectively.
Let us move on now to the next topic, just click here! Lesson 3 Monomials and Polynomials
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