Page 38 - WCS - Electrical

WORKSHOP CALCULATION & SCIENCE - CITS

4 Subtract 18x from 7x
= 7x - (18x)
= 7x - 18x
= -11x

5 Subtract 3x - 2y from 4y - 2x
= (4y - 2x) - (3x - 2y)
= 4y - 2x - 3x + 2y
= 6y - 5x
Addition and subtraction
Quantities with algebraic symbols are added or subtracted by considering those terms involving same symbols
and powers.
Example
1 10x + 14 – 7y – 11a + 2x – 4 – 3y – 4a + 8
2
2
=10x + 2x – 7y – 3y – 11a – 4a + 14 – 4 + 8
2
2
=12x – 10y – 15a + 18
2
2 2x = 10, 2x + 6 = 10 + 6
3 y + 12 = 20, y + 12 – 8 = 20 – 8

4 x + 10 = 12,
x + 10 – 10 = 12 – 10
5 3x = 6, 2 x 3x = 2 x 6, 6x = 12
6 5y = 20, .
The same number may be added or subtracted to both members of an equation without changing its equality.
Each member of an equation may be multiplied or divided by the same number or symbol without changing its
equality.
The equality of an equation is not altered when the numbers or symbols are added or subtracted from both sides.
Multiplication and division by the same numbers or symbols on both sides also will not affect the equality.
Transposition of the terms of the equations
= equals to
+ plus
– minus

x multiply
÷ divided by

Concept of equality (Fig 1)
An equation can be compared to a pair of scales which always remain in equilibrium. The two sides of the
equation can fully be transposed. 9 = 5 + x may also be written as 5 + x = 9.
We must always perform the same operation on both sides of the equation to keep the equilibrium. Add or
subtract the same amount from both sides. 5 + x = 9 By adding 3 on both sides, the equation becomes 5 + x +
3 = 9 + 3 or

x + 8 = 12.
5 + x = 9 Subtract 5 from both sides then 5 + x – 5 = 9– 5.
x = 4.

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CITS : WCS - Electrical - Exercise 4