Use cutting and rearranging to connect triangle area to base and height, then use Heron's formula when only three sides are known.

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Chapters
0:00 Area begins with a rearrangement
1:31 Turning three sides into an area
3:10 The three-sides area formula and a sweep
5:26 A complete calculation and the height mistake
6:59 Fix the mistake, then practise
8:51 Final questions and next step

Full series: Grade 9 Maths · Chalkboard Lessons
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