# geometry prove

• Oct 15th 2013, 10:09 PM
parmis
geometry prove
prove it thx! (Worried)
• Oct 16th 2013, 03:32 AM
emakarov
Re: geometry prove
If it said AE/AF = CD/BD, then both cross-products would equal the area of the parallelogram.
• Oct 16th 2013, 04:27 AM
MINOANMAN
Re: geometry prove
Emakarov is right this ratio is not valid : it is valid only if ABCD is a rombus.
• Oct 16th 2013, 07:07 AM
parmis
Re: geometry prove
Quote:

Originally Posted by MINOANMAN
Emakarov is right this ratio is not valid : it is valid only if ABCD is a rombus.

ABCD is a rhombus. how should i prove this ratio?
• Oct 16th 2013, 07:23 AM
emakarov
Re: geometry prove
As I said in post #2, AE * BD = AF * CD = area of the rhombus.
• Oct 16th 2013, 07:45 AM
parmis
Re: geometry prove
Attachment 29489
in 1, question is: What fraction of the ABCD rhombus's area is the MNP Triangle's area?
• Oct 16th 2013, 08:03 AM
emakarov
Re: geometry prove
Hint: area of △MNP = area of △MPB because MP is the median. And area of △MNB = 1/2 area of MBCN.
• Oct 16th 2013, 08:10 AM
parmis
Re: geometry prove
Quote:

Originally Posted by emakarov
Hint: area of △MNP = area of △MPB because MP is the median. And area of △MNB = 1/2 area of MBCN.

I undrestand area of △MNP= area of △MPB but why area of △MNB = 1/2 area of MBCN?
why area of △BNC = 1/2 area of MBCN? http://www.qalamro.ir/smaeel/2/(24).gif
• Oct 16th 2013, 08:23 AM
emakarov
Re: geometry prove
Quote:

Originally Posted by parmis
why area of △MNB = 1/2 area of MBCN?

Because MBCN is a parallelogram and BN is a diagonal, which divides the parallelogram into two equal triangles.
• Oct 16th 2013, 08:35 AM
parmis
Re: geometry prove
Thank you very much.
someone prove rhombus's area formula that i wrote up in picture in 6#.http://www.qalamro.ir/smaeel/2/(7).gif
• Oct 16th 2013, 08:42 AM
emakarov
Re: geometry prove
Generally, you should start a new thread for each new question. People are far less likely to read through several posts to discover that there is an unanswered question in the end.