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Homework Help: Missing angle, Tan Theta?

  1. Oct 9, 2011 #1
    1. The problem statement, all variables and given/known data

    Ok, so this is really basic and i could do it at the snap of a finger liek a year ago but it's completely escaped me. Maths is too much.

    This is a right angle triangle, with the right angle on angle C. Angles are marked A, B and C. Side CB = Adjacent, Side BA = Hyp and side CA = opposite.

    A smaller triangle is sat with it's hypotenuse as side CA. It's a right angle triangle with D as the right angle, which sits on a line that travels from C to directly over A.

    a) Calculate size of angle BAC.

    Give your answer to 1 DP.

    b) Calulate length of DA.

    Give your answer to 3 sf.

    2. Relevant equations

    AB = 22cm
    AC = 10cm
    Angle ACB = angle ADC = Angle BAD = 90

    3. The attempt at a solution

    I'm stuck. It's a simple bit of knowledge I've forgotten.

    Something to do with Sineθ ?
    Last edited: Oct 9, 2011
  2. jcsd
  3. Oct 9, 2011 #2


    Staff: Mentor

    If C is the right angle, then the hypotenuse can't be CB.

    The sides of the triangle would have to be AC and BC, and the hypotenuse would be AB.

    Please give us the correct problem description.
  4. Oct 9, 2011 #3
    Oh crap, I'm sorry!

    CB is the adjacent and angle AB is the Hypotenuse.
  5. Oct 9, 2011 #4


    Staff: Mentor

    Does this change affect anything else in your problem description? If so, please edit your original post to correct anything that might be wrong. You can edit your post by clicking the Edit button.
  6. Oct 9, 2011 #5
    No, I don't think it should - I've edited whatever it may have effected
  7. Oct 9, 2011 #6


    Staff: Mentor

    Your description still doesn't make sense to me.
    The hypotenuse of the smaller triangle is CA on the larger triangle. Where is point D? It can't be on line segment CA, since that's the hypotenuse (of the smaller triangle). Angle D has to be across from the hypotenuse.

    If you can draw a picture of the two triangles, and label each angle, that would be helpful.
  8. Oct 9, 2011 #7


    User Avatar
    Science Advisor

    Do you understand that the "hypotenuse" of a right triangle is the side opposite the right angle. "angle AB is the Hypotenuse" is impossible.
  9. Oct 9, 2011 #8


    Staff: Mentor

    The OP meant side AB, but I am still not able to get a clear picture from his/her description.
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