krit.club logo

Expressions using Letter-Numbers - Pick Patterns and Reveal Relationships

Grade 7CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

•

A variable is a letter or symbol used to represent an unknown number or a quantity that can change. Common variables include x,y,z,l,nx, y, z, l, n.

•

Constants are values that do not change, such as 5,−10,125, -10, \frac{1}{2}.

•

An algebraic expression is formed by combining variables and constants using operations like addition (++), subtraction (−-), multiplication (×\times), and division (÷\div).

•

Patterns in geometry can be expressed using variables. For example, if the side of a square is ss, its perimeter is always 4×s4 \times s.

•

Number patterns can be generalized. If nn represents the position of a term in a sequence, the nthn^{th} term can often be written as an expression in nn.

•

Rules for properties of numbers such as Commutativity and Distributivity can be expressed using letter-numbers: a+b=b+aa + b = b + a and a(b+c)=ab+aca(b + c) = ab + ac.

•

Terms are added to form expressions. For example, in 4x2−3xy4x^2 - 3xy, the terms are 4x24x^2 and −3xy-3xy.

•

The numerical factor in a term is called its coefficient. In the term −7xy-7xy, the coefficient is −7-7.

📐Formulae

P=4s (Perimeter of a square with side s)P = 4s \text{ (Perimeter of a square with side } s)

P=3s (Perimeter of an equilateral triangle with side s)P = 3s \text{ (Perimeter of an equilateral triangle with side } s)

P=2(l+b) (Perimeter of a rectangle)P = 2(l + b) \text{ (Perimeter of a rectangle)}

Even Number=2n (where n is a natural number)\text{Even Number} = 2n \text{ (where } n \text{ is a natural number)}

Odd Number=2n+1 or 2n−1\text{Odd Number} = 2n + 1 \text{ or } 2n - 1

a+b=b+a (Commutative Property of Addition)a + b = b + a \text{ (Commutative Property of Addition)}

a×(b+c)=ab+ac (Distributive Property)a \times (b + c) = ab + ac \text{ (Distributive Property)}

💡Examples

Problem 1:

Observe the pattern of matchsticks used to form the letter 'L'. One 'L' requires 22 sticks, two 'L's require 44 sticks, and three 'L's require 66 sticks. Write a general rule for the number of sticks required for nn 'L's.

Solution:

2n2n

Explanation:

Since each 'L' requires 22 matchsticks, for nn such shapes, the total sticks needed is 2×n=2n2 \times n = 2n. Here nn is the variable representing the number of shapes.

Problem 2:

Find the rule for the nthn^{th} term of the number pattern: 3,6,9,12,…3, 6, 9, 12, \dots

Solution:

3n3n

Explanation:

The terms are multiples of 33. For the 1st1^{st} term (n=1n=1), 3×1=33 \times 1 = 3. For the 2nd2^{nd} term (n=2n=2), 3×2=63 \times 2 = 6. Thus, the general relationship is 3n3n.

Problem 3:

Identify the terms and their coefficients in the expression 1.2ab−2.4b+3.6a1.2ab - 2.4b + 3.6a.

Solution:

Terms: 1.2ab,−2.4b,3.6a1.2ab, -2.4b, 3.6a. Coefficients: 1.2,−2.4,3.61.2, -2.4, 3.6.

Explanation:

Terms are the parts separated by ++ or −- signs. The coefficient is the numerical multiplier of the variables in each term.

Problem 4:

If the side of a regular hexagon is denoted by ll, express the perimeter of the hexagon using ll.

Solution:

6l6l

Explanation:

A regular hexagon has 66 equal sides. If one side is ll, the sum of all sides is l+l+l+l+l+l=6ll + l + l + l + l + l = 6l.