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Course: Basic geometry and measurement>Unit 1

Lesson 6: Perimeter intro

Finding missing side length when given perimeter

The video illustrates how to find the lengths of unknown sides on a shape by using the given perimeter and the lengths of known sides. Two examples are given, and in each case, the missing side lengths are determined to be 5 units. Created by Lindsay Spears.

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• i just wanted to ask that in the previous task you asked a question what is the perimeter of a pentagon which is of 5 units so pentagon are of many kinds just it need to have 5 sides so what kind of pentagon is it
• Yes it is not always necessary that all the sides of the pentagon are equal, but when it is mentioned as "regular" pentagon (which I think they would've in your task), then all the sides are equal.
Hope this helps :)
• If for example, the given lengths are 10,6,5,3,and1, but then one whole section is unknown. What would be the given length?
• Without knowing the total perimeter length it is impossible to determine length of the missing section.
• this really helps i always had trouble with these.
• Yes, they are very good at explaining what the problem is and what you need to do to get the answer. Go Khan Academy! They are very thorough...
• I'm in third grade at the begining of the school year it was hard but now it's pretty easy you'll get it.
• This is too easy, when will I get harder problems?
• The last question can't you just write an equation 22 + 2x = 32, because one side is 11 and the opposite side is equal so we get 22 and we have 2 sides x that we need to know, and just solve you would get x = 5 and both sides are congruent so both missing sides would be 5.