Heron's Formula
When only the three sides of a triangular plot are known, the usual half-base-times-height rule cannot start. Chapter 10, Heron's Formula, of the NCERT Mathematics textbook for Class 9 gives the remedy: from the semi-perimeter you compute the area directly. You will apply the formula to triangles of every shape and extend it to quadrilaterals by splitting them along a diagonal. Problems on land measurement and park design show surveyors and planners using the same steps you practise here.
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