Geometry Gallery (polygon review)

Geometric formulae, word problems, theorems and proofs, etc.
teddybear101
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Joined: Tue Jan 12, 2010 5:54 pm
Location: Atlana, GA (cobb county)
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Geometry Gallery (polygon review)

if given a rhombus ABCD. the perimeter of ABCD is 80 cm, CD=2x+6. find x. can i have help findinga place where i can learn this type of information. also help with this problem?

little_dragon
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Re: Geometry Gallery (polygon review)

look up the def of a "rhombus"
what does it say abt the sides?
use this to find x
4(2x+6)=80

teddybear101
Posts: 30
Joined: Tue Jan 12, 2010 5:54 pm
Location: Atlana, GA (cobb county)
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Re: Geometry Gallery (polygon review)

ok, well i have tryed to solve and ended up with answer 7. is this correct ?

Armando
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Joined: Fri Sep 17, 2010 10:04 pm
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Re: Geometry Gallery (polygon review)

You have a rhombus ABCD. AB+BC+CD+DA = 80. CD = 2x+6.

Since all sides of a rhombus are equal, you can set up the equation:

$4(2x+6)=80$

Distribute:

$8x + 24 = 80$

Subtract 24

$8x = 80 - 24$

Divide by eight:

$x = \frac {80-24}{8}$

Simplify:

$x = \frac{56}{8}$
$x = 7$

Let's check it by plugging it into the original equation.

$4(2*7+6)=80$
$4(14+6) = 80$
$4(20) = 80$
$80 = 80$

7 is correct.