Equations-Equations and Formulas
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المرجع الالكتروني للمعلوماتيه
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www.almerja.com
الجزء والصفحة:
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12-3-2017
2060
What is an Equation?
An equation says that two things are equal. It will have an equals sign "=" like this:
That equations says: what is on the left (x + 2) is equal to what is on the right (6)
So an equation is like a statement "this equals that"
What is a Formula?
A formula is a special type of equation that shows the relationship between different variables.
(A variable is a symbol like x or V that stands in for a number we don't know yet).
Example: The formula for finding the volume of a box is:
V = lwh
V stands for volume, l for length, w for width, and h for height.
When l=10, w=5, and h=4, then V = 10 × 5 × 4 = 200
A formula will have more than one variable.
These are all equations, but only some are formulas:
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x = 2y - 7
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Formula (relating x and y)
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a2 + b2 = c2
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Formula (relating a, b and c)
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x/2 + 7 = 0
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Not a Formula (just an equation)
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Without the Equals
Sometimes a formula is written without the "=":
Example: The formula for the volume of a box is:
lwh
But in a way the "=" is still there, because you could write V = lwh if you wanted to.
Subject of a Formula
The "subject" of a formula is the single variable (usually on the left of the "=") that everything else is equal to.
Example: in the formula
s = ut + ½ at2
"s" is the subject of the formula
Changing the Subject
One of the very powerful things that Algebra can do is to "rearrange" a formula so that another variable is the subject.
Rearrange the volume of a box formula (V = lwh) so that the width is the subject:
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Start with:
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V = lwh
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divide both sides by h:
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V / h = lw
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divide both sides by l:
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V / hl = w
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swap sides:
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w = V / hl
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So now if you have a box with a length of 2m, a height of 2m and a volume of 12m3, you can calculate its width:
w = V / hl
w = 12m3 / (2m×2m) = 12/4 = 3m
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