8th Class

Linear Equations in One Variable   FUNDAMENTAL In the GMO Class VII Excellence Book, Chapter 4, we had learnt about linear equations and their solutions. However, we will review these facts again and also take up new types of linear equations.   Equation: An equation is a statement of equality of two algebraic expressions involving one or more unknown quantities called variables. An equation involving only linear polynomials is called a linear equation. Some example of linear equations are given below: (i) \[2x-3=6-2x\]             (ii) \[2\left( y-3 \right)=10\] (iii) \[\frac{7}{3}m=14\]             (iv) \[91z=182\]   Rules for solving a linear equation (i) We can add the same number on both sides of the equation. For e.g., We can add 3 on both sides of \[2x-3=6-2x\] (See examples above) to get \[2x=9-2x\]   (ii) We can subtract the same more...

QUADRILATERALS   FUNDAMENTAL            Polygons: A simple closed figure made up of line segments only, is known as a polygon.
  • Minimum no of sides in a polygon is three, which gives a triangle (a).
  • More than three sides of polygon are as follows:
  • 4-sided figure = quadrilateral
  • 5 -sided figure = pentagon
  • 6-sided figure = hexagon and so on.
  Type of polygons
  • Convex polygon: Polygon in which each angle is less than 180°
e.g.:  
  • Concave Polygon : Polygon in which at least one angle is more than \[\mathbf{180}{}^\circ \]
e.g.:   According more...

SQUARE & SQUARE ROOTS   FUNDAMENTALS Square and Square Root
  • Square: If a number is multiplied by itself, the product so obtained is called the square of that number.
  • For a given number x, the square of x is\[\left( x\times x \right)\], denoted by\[{{x}^{2}}\].
e.g., \[{{\left( 4 \right)}^{2}}=4\times 4=16,{{\left( 5 \right)}^{2}}=5\times 5=25,{{\left( 12 \right)}^{2}}=12\times 12=144\] Perfect squares or Square number;"
  • A perfect square is a number that can be expressed as the product of two equal integers.
  • It is always expressible as the product of equal factors.
e.g., \[144=2\times 2\times 2\times 2\times 3\times 3={{4}^{2}}\times {{3}^{2}}={{(12)}^{2}}\] \[81=3\times 3\times 3\times 3={{3}^{2}}\times {{3}^{2}}={{\left( 9 \right)}^{2}}\] Example:- Show that 300 is not a perfect square. Solution:- Resolving 300 into prime factors, we get \[300=2\times 2\times 5\times 5\times 3\] Making pairs of equal factors, we find that the digit 3 is more...

CUBE & CUBE ROOTS   FUNDAMENTALS Cube and cube root
  • Cube:- If y is a non-zero number, then \[y\times y\times y\] written as y3 is called the cube of y or simply y cubed.
e.g.,   (i) \[{{\left( 5 \right)}^{3}}=5\times 5\times 5=125.\] Thus, Cube of 5 is 125. (ii) \[{{\left( 9 \right)}^{3}}=9\times 9\times 9=729\]. Thus,
  • Perfect cube:- A natural number n is a perfect cube if it is the cube of some natural number.
Or Natural number n is a perfect cube if there exists a natural number whose cube is n i.e. \[n={{x}^{3}}\] e.g.,(i) 343 is a perfect cube, because there is a natural number 7 such that \[343=7\times 7\times 7={{7}^{3}}\] e.g., (ii) \[{{4}^{3}}=4\times 4\times 4=64\] \[{{5}^{3}}=5\times 5\times 5=125\] \[{{9}^{3}}=9\times 9\times 9\times =723\]   Properties of perfect cube:

COMPARING QUANTITIES   FUNDAMENTALS Ratio and Proportion
  • Ratio is method of comparing two quantities of the same kind by division.
  • A ratio does not have any unit, it is only a numerical value.
  • The symbol used to write a ratio is ':' and is read as 'is to
  • A ratio is generally expressed in its simplest form.
  • To express two terms in ratio, they should be in the same units of measurement.
  • Multiplying or dividing the terms of a ratio by the same number gives equivalent ratio.
  • When two ratios are equal, they are known to be in proportion. The symbol for proportion is ': :' and is read as 'as to'.
For e.g., 2 is to 3 as to 6 is to 9 is written as 2 : 3 : : 6 : 9 or, \[\frac{2}{3}=\frac{6}{9}\]

 ALGEBRAIC EXPRESSION & IDENTITIES   FUNDAMENTALS In our GMO Class VII, We have learnt about the addition and subtraction of algebraic expressions. We will carry those ideas further.   Addition of Algebraic Expressions While adding algebraic expressions, we collect the like terms and add them. EXAMPLE 1. Add: \[\left( 2m+3n+59\text{ }and-n-p+6q+3m \right)\] Solution: Writing the terms of the given expressions in the same order in form of rows with like terms below each other and adding column wise, we get:   Example 2- Add: \[9{{x}^{3}}+6{{x}^{5}}-8+16{{x}^{2}}\] and \[10{{x}^{8}}6{{x}^{2}}+9{{x}^{3}}-3x\] Solution: Writing the given expressions in descending powers of x in the form of rows with like terms below each other and adding column wise, we get:   Subtraction of Algebraic Expressions Steps:
  • Arrange the terms of the given more...

MENSURATION   FUNDAMENTALS
  • Cuboid:- A cuboid is a solid bounded by the rectangular plane regions. A cuboid has six faces, 12 edges and 8 vertices.
Total surface Area of the cuboid \[=2\left( lb+bh+hl \right)\] sq. units. Volume of the cuboid \[={{l}^{2}}\times b\times h\] Diagonal of the cuboid \[=\sqrt{{{l}^{2}}+{{b}^{2}}+{{h}^{2}}}\]  
  • Cube:- A cuboid whose length, breadth and height are equal is called a cube.
If length of each edge of a cube is a. Then, volume of the cube \[={{a}^{3}}\] Total surface area of the cube \[=6{{a}^{2}}\] Diagonal of the cube\[=\sqrt{3a}.\]  
  • Cylinder:- It is formed by rotating one side of a rectangle about its opposite side.
Volume of the cylinder \[=\pi {{r}^{2}}h\] Area of more...

EXPONENTS & POWERS   FUNDAMENTALS Exponent:-
  • The exponent of a number says how many times it should be used in a multiplication.
Example:- \[3\,in\,{{2}^{3}}\Rightarrow {{2}^{3}}=2\times 2\times 2;\]             \[5\,in\,{{2}^{5}}\Rightarrow {{2}^{5}}=2\times 2\times 2\times 2\times 2\]
  • Exponent is also called power or index or indices
  • \[{{x}^{y}}\]can be read as yth power of x (or) x raised to the power y.
  • \[2\times 2\times 2\times 2\times 2={{2}^{5}}\],
Here \[2\times 2\times 2\times 2\times 2\] is called the product form (or) expanded form and \[{{2}^{5}}\] is called the exponential form.
  • Product Rule:- \[{{a}^{m}}\times {{a}^{n}}={{a}^{m+n}}\] (Where \[a~\ne 0\]be any rational number and m, n be rational numbers)
Example:- \[{{2}^{5}}\times {{2}^{6}}={{\left( 2 \right)}^{5+6}}={{2}^{11}}\]
  • Quotient Rule:- \[\frac{{{a}^{m}}}{{{a}^{n}}}~={{a}^{m-n}}\] (Where \[a~\ne 0\]be any rational number )
  • Example:- \[{{5}^{6}}\div {{5}^{3}}={{5}^{6-3}}={{5}^{3}}\]
  • \[{{({{a}^{m}})}^{n}}={{a}^{m\times n}}\] (Where m, n are rational numbers, \[a~\ne 0\])
more...

Direct & Inverse Proportional (Time & Work)   FUNDAMENTALS Let 3 pens cost Rs. 9, then 6 pens will cost Rs. is Clearly. More pens will cost more. Again, if 2 women can do a piece of work in 7 hours, then 1 woman alone can do it in 14 hours. Thus, less people at work, more will be the time taken to finish it. Thus, change in one quantity brings a change in the other.   Variation: If two quantities depend upon each other in a way such that the change in one results in a corresponding change in the other, then the two quantities are said to be in variation. This variation may be direct (i.e. increase in one quantity leads to increase in other quantity) as illustrated in the example of "cost of pens" above. Variation may also be indirect (i.e. more...

FACTORIZATION   FUNDAMENTALS FACTORS: When an algebraic quantity can be expressed as the product of two or more algebraic quantities, then each of these quantities is called a factor of the given algebraic quantity and the process of finding factors, is called FACTORIZATION. Remarks: Factorization is the opposite process of multiplication, EXAMPLE Look at the examples given below:
Multiplication Factorization (opposite of multiplication )
(1) \[2x\left( 3x-2y more...

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