Question 551241
sin 25° = sin155°
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155° is in the 2nd quadrant, and has a reference angle of 180°-155° = 25°
and the sine is positive in both the 1st and 2nd quadrants.  So the answer is
yes
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tan 20° = cot 70°
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Yes because 
1. cotangent and tangent are cofunctions of each other, 
2. Co-functions of complementary angles are equal.
3. 20° and 70° are complementary because their sum is 90°
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sin&#415; = cos(90-&#415;)
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Yes, because
1. cosine and sine are cofunctions of each other, 
2. Co-functions of complementary angles are equal.
3. &#415;° and 90°-&#415; are complementary because their sum is 90°
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tan&#415; = -cot(90-&#415;)
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No, because
1. cotangent and tangent are cofunctions of each other, 
2. &#415;° and 90°-&#415; are complementary because their sum is 90°
3. Co-functions of complementary angles are equal, so one 
cannot have the opposite sign from the other!
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sin&#415; = 1/csc&#415;, where sin&#415; is not 0
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Yes, because sine and cosecant are reciprocal trig functions.
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cos&#415; = 1/sec&#415;, where cos&#415; is not 0
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Yes, because cosine and secant are reciprocal trig functions.
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sin&#415; is never greater than 1 or less than -1
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True because the sine is {{{opposite/hypotenuse}}} and the opposite is
never greater than the hypotenuse.

Edwin</pre>