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math:)

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If the given point is on the terminal arm of an angle A in standard position, angle A is greater than or equal to 0 degrees and it is less than or equal to 180 degrees, find the measure of angle A, to the nearest tenth of a degree.
a) (4,3)
b) (12,5)
c) (-6,8)
d) (-24,7)

PLEASE help me!! with the steps and all i have no idea about this... thankyou so much!!

  • math:) -

    If you are just learning this, I suggest you make a sketch of the right-angled triangle
    a) and b) will be in quadrant I
    c) and d) will be in quadrant II

    I will do b) and c)

    b) by Pythagoras, it is easy to find the hypotenuse to be 13
    since cosØ = 12/13
    use the cosine inverse of your calculator...
    enter:
    2nd
    cos
    (12÷13)
    = to get appr 22.62° or 23°

    c) hypotenuse^2 = (-6)^2 + 8^2 = 100
    hypot = √100 = 10
    cosØ = -6/10 = -3/5 or -.6

    enter:
    2nd
    cos
    (-.6)
    =
    to get 126.87° or 127°

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