Posted by **Mary** on Tuesday, November 13, 2007 at 8:29pm.

I am trying to help my son in Algebra, the only thing is that I have forgot some of these thing.He has a word problem I can not figure it out please help a mother help her 9th grader.

Q- The polygons below are similar. Find the unknown side lengths if c=24. Each measure is in centimeter. Express you answers in decimals. The Diagram measures 16,20,24,28. Please help how to figure this out. I think the formula is 180(x-2) is this correct and if so do I do the following 180(24-2) which = 180(22)=3960 I do not know how to put it in decimals.

- Math -
**Reiny**, Tuesday, November 13, 2007 at 8:36pm
One of the problems here is that we can't show diagrams.

When you say "The polygons below are similar", we can't know what shapes you are describing.

From the 4 sides you give, I would assume you have a quadrilateral (4 sides), but I don't know what you are trying to find, is it angles?

the formula 180(n-2) is for the sum of the interior angles of a polygon, where n is the number of sides.

by doing 180(22)=3960 you found the sum of the inside angles of a 24 sided figure, somehow I don't think that is what you wanted.

- Math -
**Mary**, Tuesday, November 13, 2007 at 8:46pm
it is a four sided where 16 is replaced by c=24 and d=20,e=24,f=28. It goes and on and ask to find the unknown side lenghts if c=24. Each measure is in centimeter. Express your answers in decimals. That is the whole question.

- Math -
**Reiny**, Tuesday, November 13, 2007 at 8:54pm
One of the properties of similar figures is that corresponding sides are in the same ratio.

are you saying that the value of 16 in the first figure is now 24 in the new one?

If so, then form the ratio 24/16 and set it equal to the fraction for another matching pair of sides.

eg. perhaps you want to find the side of the first figure that matches with the sides labeled 20 in the second

put 24/16 = 20/x

cross-multiply 24x = (16)(20)

x = 13 1/3

Hope this helps

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