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For Class 8, 9 & 10

Foundation - a strong base in Physics, Chemistry, Maths & Biology

Concept-first questions with clear model answers across all four subjects, aligned to NCERT. Start early, build the habit, and walk into your board exams, NEET and JEE already ahead.

Class 824Class 924Class 1036
SubjectAllPhysics 19Chemistry 19Biology 19Mathematics 27
ChapterAllAtoms and MoleculesForce and Laws of MotionGravitationHeron's FormulaImprovement in Food ResourcesIs Matter Around Us PureLinear Equations in Two VariablesMatter in Our SurroundingsMotionNatural ResourcesNumber SystemsPolynomialsSoundStatisticsStructure of the AtomSurface Areas and VolumesThe Fundamental Unit of LifeTissuesWork and Energy

Showing 1 question for Class 9. Tap a card to reveal the answer.

MathematicsHeron's Formulamedium

Find the area of a triangle whose sides are 3 cm, 4 cm and 5 cm using Heron's formula.

Reveal answer ↓

What it is

Heron's formula finds a triangle's area from just its three sides, using the semi-perimeter.

Answer

First find the semi-perimeter s = (3 + 4 + 5)/2 = 6 cm. Heron's formula gives Area = sqrt[s(s - a)(s - b)(s - c)] = sqrt[6(6 - 3)(6 - 4)(6 - 5)] = sqrt[6 x 3 x 2 x 1] = sqrt[36] = 6 square cm.

Area = sqrt[s(s-a)(s-b)(s-c)], s = (a+b+c)/2

  • •s = (a + b + c)/2 = 6 cm
  • •Area = sqrt[s(s-a)(s-b)(s-c)]
  • •= sqrt[36] = 6 cm^2

Why learn this

It measures land, plots and any triangle where you cannot easily find the height.

💡 Memory trick

Half the perimeter is 's'; Area = sqrt of s times the three (s - side) gaps.