1. ## geometry prove

prove it thx!

2. ## Re: geometry prove

If it said AE/AF = CD/BD, then both cross-products would equal the area of the parallelogram.

3. ## Re: geometry prove

Emakarov is right this ratio is not valid : it is valid only if ABCD is a rombus.

4. ## Re: geometry prove

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?

5. ## Re: geometry prove

As I said in post #2, AE * BD = AF * CD = area of the rhombus.

6. ## Re: geometry prove

in 1, question is: What fraction of the ABCD rhombus's area is the MNP Triangle's area?

7. ## Re: geometry prove

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

8. ## Re: geometry prove

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?

9. ## Re: geometry prove

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.

10. ## Re: geometry prove

Thank you very much.
someone prove rhombus's area formula that i wrote up in picture in 6#.

11. ## 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.