Results 1 to 5 of 5

Math Help - Trigno problem. Expressing values in terms of and showing...

  1. #1
    Junior Member
    Joined
    Jan 2011
    Posts
    35

    Trigno problem. Expressing values in terms of and showing...

    Me again.

    Okay, for this question that I'm having difficulty in, here is the figure:



    And as we know:

    sin30= under.root (1/4)
    cos30= under.root (3/4)

    This question is divided into 2 parts.

    i) express each of AC and BC exactly in terms of L, and show that
    AB=(1/2)L under.root7. (Note: how do I write mathematical symbols in this forum?)

    I used pythagoras method and sin30=perpendicualr/hypotenuse to get values of DC and AC, but the problem is, they are coming as fraction under.root values rather then whole numbers. This wouldn't be a problem if there weren't any conditions to have under.root solutions. E.g, I'm getting AC as L under.root 3/4. I then have to apply THIS to get DC and subsequently, BC (twice DC), from pythag method. DC comes as (1/2)L therefore BC becomes L. Is this correct?

    ii) Even though I was able to prove AB as (1/2)L under.root7, when applying in this part of the question, it doesn't work. Here is says: Show that x=tan^-1(2/under.root3) -30.

    I'm doing this like this: tan (x+30) = BC/AC

    tan (x+30) = L/L under.root (3/4).
    x = tan^-1 [L/L under.root (3/4)] -30

    this is wrong but I do not know how to solve this. How do I do this?
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Member
    Joined
    Oct 2010
    From
    Heart of Winter
    Posts
    115
    Thanks
    1
    ...
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Member
    Joined
    Oct 2010
    From
    Heart of Winter
    Posts
    115
    Thanks
    1
    you put maths in a post with 'latex' tags. you should read the latex help forum. and if you click on a latex equation in a post the code pops up for you also. I will let someone else answer your question I am to new to give you the correct advice.
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor

    Joined
    Apr 2005
    Posts
    15,693
    Thanks
    1466
    This forum uses [ math ] and [ /math ] (without the spaces) to begin and end LaTex. the code for "root" is \sqrt{x} so, for example, [ math ]\sqrt{x}[ /math ] (again without the spaces) gives \sqrt{x}. Click on any LaTex to see the code used.

    Now for your problem. Yes, sin(30)= \frac{1}{2} and cos(30)= \frac{\sqrt{3}}{2} so that tan(30)= \frac{\frac{1}{2}}{\frac{\sqrt{3}}{2}}= \frac{1}{\sqrt{3}}.

    Take the "opposite" side of the smaller triangle to be "1" and the "near" side to be \sqrt{3}. Then the larger triangle has "opposite" side of length 2 and "near" side of length \sqrt{3} so that tan(x+ 30)= \frac{2}{\sqrt{3}} . You can find x+ 30= arctan(\frac{2}{\sqrt{3}}) and solve for x from that.

    Those will NOT be whole numbers.

    tan (x+30) = L/L under.root (3/4).
    This is incorrect. You multiplied when you should have divided.
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Junior Member
    Joined
    Jan 2011
    Posts
    35
    Thanks for that detailed explanation.

    I had completely forgotten that under.root(3/4) could be written as (under.root 3)/2. That clears it. Problem solved.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Expressing x in terms of y
    Posted in the Pre-Calculus Forum
    Replies: 6
    Last Post: August 18th 2009, 07:29 AM
  2. Expressing Sin(2p) in terms of x
    Posted in the Trigonometry Forum
    Replies: 4
    Last Post: January 28th 2009, 01:49 AM
  3. Expressing In Terms of a And b
    Posted in the Algebra Forum
    Replies: 3
    Last Post: January 15th 2009, 07:14 PM
  4. Expressing in terms of sin.
    Posted in the Trigonometry Forum
    Replies: 3
    Last Post: December 16th 2008, 09:30 AM
  5. Expressing in terms of X
    Posted in the Math Topics Forum
    Replies: 2
    Last Post: November 9th 2008, 01:08 PM

Search Tags


/mathhelpforum @mathhelpforum