# Mathematics Class 9

## Mean and Median

The mean value of a variable is defined as the sum of all the values of the variable divided by the number of values. The mean of ungrouped or raw data is given by Mean =sum of observations/Number of observations. Mean and Median PDF Download PDF

## Construction of Polygons

A quadrilateral can be constructed when the following measurements are given:(i) Four sides and one diagonal(ii) Three sides and two diagonals(iii) Four sides and one angle(iv) Three sides and two consecutive angles Construction of Polygons PDF Download PDF

## Mid-Point and Intercept Theorems

Midpoint Theorem: The line segment joining the midpoints of any two sides of a triangle is parallel to the third side andequal to half of it. Converse of Midpoint Theorem: The straight line drawn through the middle point of one side of a triangle parallel to another side bisects the third side. Equal Intercept Theorem:

## Congruent Triangles

A triangle is a simple closed figure made up of three line segments. A triangle has six parts or elements, namely: a) Three sides and b) Three angles. The point of intersection of two adjacent sides of a triangle is called a vertex. A triangle has 3 vertices. A median of a triangle is the

## Linear Equations in One Variable

An equation is a statement that relates two expressions with an equality sign. The equation in which the variable is of the first order is called a simple or a linear equation. To solve a problem based on equations, first translate the relation given in the problem into an algebraic equation and then solve the

## Rational and Irrational Numbers

Every integer (positive, negative, or Zero) and every decimal number is a rational number. All terminating and non-terminating but repeating (or periodic or recurring) decimals are rational numbers. The real numbers, which are not rational, are called irrational numbers. The square roots, cube roots, etc. of natural numbers are irrational numbers; if their exact value

## Distance Formula

The points A, B, and C are collinear if AB + BC = AC. Three points A, B, and C are the vertices of an equilateral triangle if AB = BC = CA. Points A, B, and C are the vertices of an isosceles triangle if AB = BC or BC = CA, or CA

## Circle

A circle is a locus of a point that moves in such a way that its distance from a fixed point is always constant. The fixed point is called the center of the circle. The line segment joining any two points on a circle is called a chord of the circle. A chord of a

## Surface Area and Volume of 3-D Solids

Anything which occupies space and has a definite shape is called a solid. The surface area of a solid is the sum of the areas of all its faces. The space occupied by a solid object is the volume of that object. Surface Area and Volume of 3-D Solids PDF Download PDF

## Statistics

Facts or figures collected with a definite purpose are called data. Statistics deals with collection, presentation, analysis, and interpretation of numerical data. Arranging data in order to study their salient features is called the presentation of data. Data arranged in ascending or descending order is called arrayed data or an array. The range of the

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