8:36 Finding the Missing Side of a Rectangle Given the Area | Math with Mr. J
Two clear worked examples finding a rectangle's missing side by dividing the area.
Find missing length given area
Calculate a missing length, given the area
4 hand-picked video lessons for this topic, each checked for relevance and clarity, graded by difficulty and labelled by depth. Press play to watch — nothing loads from YouTube until you do.
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4 shown 8:36 
4:26 How to Find the Missing Side Length of a Rectangle when you know the Area
Short, friendly walkthrough of dividing area by one side to find the missing length.
3:37 Finding the missing length on a rectangle when given the area
Quick, clear demo of rearranging area = length x width to find a missing side.
16:04 Area of Shapes - GCSE Maths
Covers all area formulas then shows how to work backwards to a missing length.
Jump to 13:21Finding missing lengths