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Math Help - Help me figure out area of triangle!!

  1. #1
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    Smile Help me figure out area of triangle!!

    hey everyone , i would like you please to help me figure out 2 problems they both about figuring out the area of each a triangle ABC and an engineer estimated area of vertical cross section of water flowing under bridge. and there is a model for it .

    regards
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  2. #2
    Bar0n janvdl's Avatar
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    Quote Originally Posted by carlasader View Post
    hey everyone , i would like you please to help me figure out 2 problems they both about figuring out the area of each a triangle ABC and an engineer estimated area of vertical cross section of water flowing under bridge. and there is a model for it .

    regards
    6.a)  \frac{Sin B}{b} = \frac{Sin C}{c}

     \frac{c Sin B}{b} = Sin C

     C = 52,47 \ degrees

    6.b) Now angle A = 180 - (B + C)
    Thus A = 52,53 degrees

    Im going to work out the area now. Im just struggling a bit with it.
    Last edited by janvdl; May 26th 2007 at 09:54 AM.
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  3. #3
    Bar0n janvdl's Avatar
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    6.c) Yes I got it!!!
    Draw a line AM from A to BC, but perpendicular to BC.
    So that B = 75 degrees ; A = 15 degrees ; M1 = 90 degrees

    Then we can say that  cos \ 75 = \frac{BM}{AB}

    And then BM is 2,02

    With Pythagoras we determine that AM(the height) = 7,534

    With pythagoras again, we determine the full length of BC(the base) to be: 7,81

     Area = \frac{1}{2} (7,81) (7,534) = 29,408 \ square \ units
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  4. #4
    Bar0n janvdl's Avatar
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    May i please have a picture of how the bridge looks? Im bad at visualising things.
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  5. #5
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    Hello, carlasader and Jhevon!


    Are you familiar with this formula for the area of a triangle?

    . . Area \:=\:\frac{1}{2}\ bc\sin A

    The area is one-half the product of two sides times the sine of the included angle.


    We have: . b = AC = 9.5,\:c = AB = 7.8,\:\angle A = 52.5^o

    Hence: . Area \:=\:\frac{1}{2}(9.5)(7.8)\sin52.5^o \:\approx\:29.4

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  6. #6
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    Quote Originally Posted by carlasader View Post
    hey everyone , i would like you please to help me figure out 2 problems they both about figuring out the area of each a triangle ABC and an engineer estimated area of vertical cross section of water flowing under bridge. and there is a model for it .

    regards
    hello,

    to #7:

    if a is the lower bound of the area,
    if b is the upper bound of the area,
    if n is the number of trapezoids
    then the trapezoid formula to estimate the value of an area is:

    A \approx \frac{b-a}{2n}(y_a + 2y_1 + 2y_3 + \ldots +2y_{n-1} + y_b)

    With your values you get:

    A \approx \frac{24-0}{2 \cdot 6}(1.2 + 2 \cdot 2.3 + 2 \cdot 3.8 + \ldots +2 \cdot 1.9 + 0.6)= 68 \ m^2
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  7. #7
    Bar0n janvdl's Avatar
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    Thank you to Soroban, I completely forgot that Area formula, and once again, took a long way around.

    And thank you to Earboth, i also understand that problem better now. A little bit anyway
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  8. #8
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by Soroban View Post
    Hello, carlasader and Jhevon!

    lol, I wasn't even here Soroban I think you meant to say "carlasader and janvdl"
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