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mayankdevnani

Two adjacent sides of a parallelogram are 51 cm and 37 cm. One of its diagonals is 20 cm, then its area is..... a) \[412 cm^2\] b) \[512 cm^2\] c) \[612 cm^2\] d) \[712 cm^2\]

  • one year ago
  • one year ago

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  1. sauravshakya
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    Use herons formula to calculate the area of one half of the parallelogram.

    • one year ago
  2. sauravshakya
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    |dw:1354886905111:dw|

    • one year ago
  3. sauravshakya
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    |dw:1354886978203:dw|

    • one year ago
  4. mayankdevnani
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    |dw:1354887034102:dw|

    • one year ago
  5. chihiroasleaf
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    yes.., s = 54, then what is the area of the triangle?

    • one year ago
  6. sauravshakya
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    Good going

    • one year ago
  7. mayankdevnani
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    |dw:1354887176565:dw|

    • one year ago
  8. chihiroasleaf
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    yup..., now simplify ...

    • one year ago
  9. mayankdevnani
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    |dw:1354887394948:dw|

    • one year ago
  10. mayankdevnani
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    now, then multiply it by 2 to get 612 cm^2. so option c is right answer.....right???

    • one year ago
  11. chihiroasleaf
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    right... :)

    • one year ago
  12. mayankdevnani
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    right? @chihiroasleaf and @sauravshakya

    • one year ago
  13. mayankdevnani
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    any short method!!!!

    • one year ago
  14. mayankdevnani
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    @hartnn @sirm3d @amistre64 @AravindG @AccessDenied any short method!!!to solve this question!!!

    • one year ago
  15. mayankdevnani
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    @DLS @satellite73 @nubeer plz help me!!!

    • one year ago
  16. DLS
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    if u were given the co-ordinates then I would've given u a shorter method

    • one year ago
  17. mayankdevnani
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    no, i am in 9 class its very long method

    • one year ago
  18. DLS
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    -_-

    • one year ago
  19. mayankdevnani
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    anyways!!! thnx...

    • one year ago
  20. scarydoor
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    I may have a way of calculating those coordinates quickly: |dw:1354889186448:dw| \[x^2+y^2=c^2\\x^2+(y-a)^2=b^2\\x^2+y^2+a^2-2ay=b^2\\c^2+a^2-2ay=b^2\\y=\frac{b^2-c^2-a^2}{2a}\\x=\sqrt{\frac{b^2-a^2}{-2a}}\]

    • one year ago
  21. scarydoor
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    So now you know the coordinates of the parallelogram. There is a formula from algebra about how to calculate the area. It involves cross products or inner products or something?

    • one year ago
  22. scarydoor
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    http://en.wikipedia.org/wiki/Parallelogram#The_area_on_coordinate_system

    • one year ago
  23. scarydoor
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    If you had good memory, you could just memorise the formula for x and y that I derived above. (I think it's right...) Then calculating the area would take about three lines.

    • one year ago
  24. mayankdevnani
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    thnx... @scarydoor

    • one year ago
  25. scarydoor
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    actually the formula for x might be slightly off.... but it can be fixed I think.

    • one year ago
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