There are several important formulas that students in CBSE Class 7 Mathematics should memorize. These formulas are essential for solving various mathematical problems and understanding different concepts.

1. Basic Arithmetic Formulas:
- Addition: a + b = c
- Subtraction: a - b = c
- Multiplication: a × b = c
- Division: a ÷ b = c

2. Algebraic Formulas:
- Distributive Property: a × (b + c) = a × b + a × c
- Identity Property of Addition: a + 0 = a
- Identity Property of Multiplication: a × 1 = a
- Commutative Property of Addition: a + b = b + a
- Commutative Property of Multiplication: a × b = b × a
- Associative Property of Addition: (a + b) + c = a + (b + c)
- Associative Property of Multiplication: (a × b) × c = a × (b × c)

3. Geometry Formulas:
- Perimeter of a Rectangle: 2 × (length + width)
- Area of a Rectangle: length × width
- Circumference of a Circle: 2 × π × radius
- Area of a Circle: π × radius^2
- Perimeter of a Triangle: a + b + c
- Area of a Triangle: (base × height) / 2
- Pythagorean Theorem: a^2 + b^2 = c^2 (for a right-angled triangle)

4. Fractions Formulas:
- Adding Fractions: (a/b) + (c/d) = (ad + bc) / bd
- Subtracting Fractions: (a/b) - (c/d) = (ad - bc) / bd
- Multiplying Fractions: (a/b) × (c/d) = (a × c) / (b × d)
- Dividing Fractions: (a/b) ÷ (c/d) = (a/b) × (d/c)

5. Percentage Formulas:
- Percentage: (part / whole) × 100
- Increase Percentage: (new value - old value) / old value × 100
- Decrease Percentage: (old value - new value) / old value × 100

6. Statistics Formulas:
- Mean: Sum of all numbers / Total number of numbers
- Median: Middle value of a given set of numbers (when arranged in ascending order)
- Mode: Most frequently occurring value in a given set of numbers

It is important for students to practice these formulas regularly to strengthen their mathematical skills.