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Trig Question - what did i do wrong? (1 Viewer)
- Thread starter smith93
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What an interesting question....
Cos (theta) cant equal to zero unless the angle we are looking at are 90 or 270 degrees. However because the question says is is larger than 90 degrees (and hence must be less than 180 degrees), cos(theta) cant equal to 0.
But in saying that i cant see why option (d) isnt also a possible answer.
Perhaps Carrot can explain?
Cos (theta) cant equal to zero unless the angle we are looking at are 90 or 270 degrees. However because the question says is is larger than 90 degrees (and hence must be less than 180 degrees), cos(theta) cant equal to 0.
But in saying that i cant see why option (d) isnt also a possible answer.
Perhaps Carrot can explain?
skillstriker
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yeh i think b,c and d are correct
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deswa1
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As theta is greater than 90, it also has to be less than 180 (angle sum of triangle)- second quadrant. It can't be 0 as cosx is zero for x=90,270 (both out of range), it can't be 0.5 because cosx is negative in the second quadrant and it can't be 1.5 because cosx is always less than 1. Maybe the question was meant to be which one can it be?
Carrotsticks
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The answer must be (B) or (C) or (D). The others are incorrect.
(A): If one of the angles is 120 degrees, then cos 120 = -0.5. Hence 120 is a possible value. Thus, A is struck out as an answer.
(B): As Peeik pointed out, the only two possible solutions are 90 or 270 degrees. However, we are told that the angle is larger than 90, so that solution is out. Furthermore, we can't have 270 because the angle sum of the triangle (on the Euclidean plane at least) is 180 degrees.
(C): The only two angles such that cos(theta) = 0.5 are 60 and 300 degrees. However, 60 is less than 90 and 300 breaks the angle sum of triangle, so neither.
(D): Impossible since cos(theta) <= 1.
Hence the answer is either (B) or (C) or (D).
(A): If one of the angles is 120 degrees, then cos 120 = -0.5. Hence 120 is a possible value. Thus, A is struck out as an answer.
(B): As Peeik pointed out, the only two possible solutions are 90 or 270 degrees. However, we are told that the angle is larger than 90, so that solution is out. Furthermore, we can't have 270 because the angle sum of the triangle (on the Euclidean plane at least) is 180 degrees.
(C): The only two angles such that cos(theta) = 0.5 are 60 and 300 degrees. However, 60 is less than 90 and 300 breaks the angle sum of triangle, so neither.
(D): Impossible since cos(theta) <= 1.
Hence the answer is either (B) or (C) or (D).