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Free study notes for CBSE & ICSE, Classes 6–12.

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MathematicsClass 9ICSE

Join Two Mid-points and You Get Exactly Half the Third Side

Prove the mid-point theorem and use it for lengths, apply the converse to identify a mid-point, use the equal intercept theorem on transversals, and show why joining the mid-points of any quadrilateral gives a parallelogram.

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MathematicsClass 9ICSE

The Longest Side Always Faces the Largest Angle

Rank a triangle's angles from its sides and its sides from its angles, test whether three lengths can form a triangle at all, prove the perpendicular is the shortest route to a line, and order the parts of a figure.

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MathematicsClass 9ICSE

Equal Sides Force Equal Angles, and the Converse Is True Too

Prove that base angles of an isosceles triangle are equal, prove the converse to show a triangle is isosceles, calculate unknown angles with the angle sum and exterior angle, and handle riders that combine both with congruence.

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MathematicsClass 9ICSE

Three Matching Parts Are Enough to Fix a Triangle Completely

Choose between SSS, SAS, AAS and RHS, write the correspondence in the right order, set out a congruence proof in logical steps, and use CPCTC to unlock unknown sides and angles.

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MathematicsClass 9ICSE

Turn Multiplication into Addition and Powers into Products

Derive the product, quotient and power laws from the laws of indices, expand a messy logarithm into separate terms, collapse a sum of logs into one, and prove identities and solve equations safely.

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MathematicsClass 9ICSE

A Logarithm Is Just the Question an Exponent Answers

Read the logarithm as the index a base needs, convert freely between exponential and logarithmic form, evaluate logs straight from the definition, and solve for a missing base or argument.

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MathematicsClass 9ICSE

A Zero Power Equals One for a Reason You Can Derive

Use the three laws of indices, work out what zero, negative and fractional powers must mean, solve equations by equating indices, and simplify expressions whose bases look different.

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MathematicsClass 9ICSE

One Formula Solves Any Pair of Equations Without Rearranging

Apply the cross-multiplication formula to any pair of linear equations, then frame equations from word problems on ages, fractions, digits, speed and the sides of a rectangle.

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MathematicsClass 9ICSE

Two Equations Pin Down Two Unknowns and One Equation Cannot

Solve a pair of linear equations by substitution and by elimination, clear fractions and brackets before you start, and check a given solution or find a missing constant from it.

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MathematicsClass 9ICSE

The Sign in the Quadratic Factor Is Always the Opposite One

Split the middle term of a quadratic whether the leading coefficient is one or not, factorise a sum or difference of cubes with the right signs, and take a composite expression apart completely.

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MathematicsClass 9ICSE

Add a Term and Take It Away Again to Reveal a Hidden Factor

Take out the highest common factor, split four or six terms into workable groups, spot a difference of two squares even when it is disguised, and manufacture one by completing the square.

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MathematicsClass 9ICSE

Find a Cubed Plus Its Reciprocal Without Ever Finding a

Expand the cube of a binomial and use it to cube 21 and 99, climb from a plus one over a to its square and cube, substitute into an identity to get a value, and prove an identity outright.

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MathematicsClass 9ICSE

Square Any Number Near a Hundred Without Writing Anything Down

Expand the square of a binomial and use it to square 103 and 97 mentally, square a three-term expression with the correct signs, expand a product of two binomials, and combine two expansions.

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MathematicsClass 9ICSE

Ten Per Cent Off for Three Years Is Not Thirty Per Cent Off

Use the amount formula for any number of years, halve the rate for half-yearly compounding, find whichever of P, r, n or A is missing, and handle population growth and machine depreciation.

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MathematicsClass 9ICSE

The Extra Money Is Interest Earned on Last Year's Interest

Work compound interest out year by year on a growing principal, handle a rate that changes each year, find exactly why compound interest beats simple interest, and work backwards to the principal or rate.

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MathematicsClass 9ICSE

Clearing a Root Out of a Denominator Makes Your Answer More Accurate

Simplify any surd to its lowest form, add, subtract, multiply and divide surds, kill the root in a denominator with its conjugate, and order surds of different index.

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MathematicsClass 9ICSE

Assume a Number Is a Fraction and Watch the Assumption Collapse

Sort numbers into rational and irrational, plot a square root on the number line by construction, prove root 2 irrational by contradiction, and turn any recurring decimal into a fraction.

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BiologyClass 9ICSE

One Body Stays Out of Politics So It Can Enter a War Zone

Learn where the Red Cross came from and what it stands for, what it actually does in India and abroad, and how the World Health Organisation works through governments instead of volunteers.

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BiologyClass 9ICSE

One Chemical Is Safe on a Wound and Deadly in the Same Bottle

Learn how a vaccine teaches the body to defend itself, why a serum works at once and briefly, where antiseptics end and disinfectants begin, and what the body's own first line of defence does.

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BiologyClass 9ICSE

Stopping a Course of Medicine Early Is How a Curable Illness Turns Resistant

Learn the symptoms and control of cholera, typhoid and tuberculosis, then AIDS, chicken pox and hepatitis, then malaria, amoebiasis and sleeping sickness, then ascariasis, taeniasis and filariasis.

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BiologyClass 9ICSE

A Fly Carries Germs on Its Legs and a Mosquito Breeds Them Inside

Separate communicable from non-communicable disease, learn what endemic, epidemic, pandemic and sporadic actually describe, follow the air-borne and water-borne routes, and control the three vectors.

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BiologyClass 9ICSE

The Part of You That Touches the World Is Already Dead

Label the epidermis and dermis and learn what each does, meet the five derivatives of the skin from sweat glands to mammary glands, and follow how vasodilation and vasoconstriction hold your temperature steady.

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BiologyClass 9ICSE

A Muscle Can Only Pull, Which Is Why Every Joint Needs Two

List what the skeleton does besides holding you up, split its 206 bones into axial and appendicular and check the count, then classify every joint and place the four movable kinds in the body.

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BiologyClass 9ICSE

Food in Your Gut Is Not Yet Inside You in Any Real Sense

Label a tooth from enamel to pulp, write the dental formula and check the count, place every digestive organ and gland with its job, then separate digestion from absorption and assimilation.

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