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Substracting equation (1) from (2) results in: \(40x = 288; x = 7.2\)

Then, from triangle DEC - \(7.2^2 + EC^2 = 12^2\) \(51.84 + EC^2 = 144\) \(EC = \sqrt{92.16}\)

We do not need to calculate we can use the answers. \(\sqrt{92.16}\) is obviously more than 9, since \(9^2 = 81\) hence the only answer suitable is \(EC = 9.6\)

Re: If ABCD is a rectangle, then what is the length of EC?
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15 Mar 2018, 18:48

We can see that Tr BAD is a right angled triangle with two sides 12 and 16. Now, we know (3, 4, 5) as a set of sides for a right angled triangle. Multiply each by 4, we get (12, 16, 20)

So, the side BD is 20.

Area of Tr BCD is half of the area of Rec ABCD

1/2*BD*EC = 1/2*AD*CD

1/2*20*EC = 1/2*12*16

EC = 9.6cm

itisSheldon wrote:

If ABCD is a rectangle, then what is the length of EC?

Attachment:

Capture1.JPG

(A) 7.8 (B) 8 (C) 8.4 (D) 9 (E) 9.6

gmatclubot

Re: If ABCD is a rectangle, then what is the length of EC? &nbs
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15 Mar 2018, 18:48