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3. If the area of a rectangle is given by the algebraic expression l × b sq. units, where l is length and
b is breadth of the rectangle, then find the area of a rectangular field whose length, l = 200 m and
b = 160 m.
4. If the perimeter of a square is given by the algebraic expression (4 × a) units, where a is length of
the equal side of the square, then find the perimeter of the square whose:
3
(a) side, a = 2 cm (b) side, a = cm.
3
4
5. If the number of sides of a regular polygon is given by the algebraic expression 360° , where q is
θ
the measure of an exterior angle, then find number of sides of and write the name of the polygon, if:
(a) q = 30° (b) q = 45° (c) q = 72° (d) q = 15°

Addition and Subtraction of Algebraic Expressions

Addition and Subtraction of Like Terms

Let us add 3x and 4x.
3x + 4x = (3 + 4) x = 7x

\ 3x + 4x = 7x
Now, let us subtract 2pq from 5pq.

5pq – 2pq = (5 – 2) pq = 3pq
\ 5pq – 2pq = 3pq
It is clear from the above, the addition or subtraction of the like terms is an another like term whose
numerical coefficient is the sum or difference of the numerical coefficients of those like terms.

Example 18: Add the following:
2 1
(a) 7xyz, 9xyz (b) 8xy, 11xy, 5xy (c) 2ab, 4ab, ab, ab
3 3
Solution: (a) 7xyz + 9xyz = (7 + 9) xyz = 16xyz

(b) 8xy + 11xy + 5xy = (8 + 11 + 5) xy = 24xy
2 1  2 1
(c) 2ab, 4ab, ab, ab = 24++ +  ab = (2 + 4 + 1) ab = 7ab

3 3  3 3
Example 19: Subtract the following:

(a) 2xz from 7xz (b) 11mn from 19mn (c) 5pq from 8pq

Solution: (a) 7xz – 2xz = (7 – 2)xz = 5xz
(b) 19mn – 11mn = (11 – 9)mn = 2mn
(c) 8pq – 5pq = (8 – 5)pq = 3pq

Addition and Subtraction of Unlike Terms

Unlike terms cannot be added or subtracted as we added like terms. For addition and subtraction
of unlike terms, the terms are connected by the appropriate sign.
For example: The sum of 2x and 3y = 2x + 3y
The sum of 3x and −4y = 3x − 4y

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