Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Finding angles

  1. Apr 21, 2004 #1
    Find the acute angle that is formed by the line y - (sqrt(3)) x + 1 = 0 and the x-axis.

    better picture here:

    I am totally lost with this one. It was from my old trigonometry test, but I don't see the relavance of the question to trigonometry :frown:
  2. jcsd
  3. Apr 21, 2004 #2

    matt grime

    User Avatar
    Science Advisor
    Homework Helper

    you know the gradient and that's tan of the angle you want
  4. Apr 21, 2004 #3
    so how would I start tackling this question :redface: ?
  5. Apr 21, 2004 #4
    What this is basically is polar coordinates.

    We solve for y, and get y = sqrt(3) - 1. It's easier to do if the graph intersects the origin. Because this is just a straight line, the -1 can be removed from the equation and it won't change the angle to the x-axis. So, our equation is...

    y = sqrt(3)x

    Next, we need to get a point. Just to keep nice even answers, I'll use x = sqrt(3).

    y = sqrt(3)x
    y = sqrt(3)*sqrt(3)
    y = 3

    So, a point is (sqrt(3), 3).

    Now, what you do is basically, it makes a triangle. The base (x) is sqrt(3), and the height (y) is 3.

    We use our SOH-CAH-TOA trig functions, and see that tan = opp/adj. The opposite angle is the height/y, and the adjacent angle is the base/x.

    I'm just using the letter t for now to make things easier...

    tan t = 3/sqrt(3)
    t = arctan(3/sqrt(3))

    t = 60 degrees, or pi/3 if you're working in radians

    NOTE: I always seem to goof something up whenever I try to help here, so someone else should just double check what I did.
  6. Apr 21, 2004 #5

    matt grime

    User Avatar
    Science Advisor
    Homework Helper

    apart from the fact that you made it far more complicated than it needs to be, that is correct.


    then the gradient is m and that is tan of the angle of the slope, that's all.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Finding angles
  1. Find the angle (Replies: 10)

  2. Finding the Angles (Replies: 21)