Find the lenghth of AB sides of ABCD parallelogram AD = (3/5)AB . Perimeter of ABCD is 11.2 cm .

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The perimeter of the parallelogram ABCD is:

AB+BC+CD+AD = 11.2

But we know that AB=CD and BC=AD

==> 2AB +2AD = 11.2

We also have AD=(3/5) AB

==>  2AB+ 2(3/5)AB=11.2

==> (16/5) AB = 11.2

==> AB = (11.2) (5/16) = 3.5

Then AD = (3/5) *3.5 = 2.1

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We know that the perimeter of this figure must be equal to the sum of 2 times each side.  So

2AD + 2 AB = 11.2

We know that AD is 3/5 of AB and 3/5 = .6.  So

AD = .6 AB

Now we substitute -- we put in .6 AB in the place of AD.

2 (.6 AB) + 2 AB = 11.2

1.2 AB + 2 AB = 11.2

3.2 AB = 11.2

AB = 3.5

So the length of the side AB is 3.5.

If AB = 3.5 and AD = .6(3.5) then

AD = 2.1

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