The cosine of an angle is defined as the sine of the complementary angle. The complementary angle equals the given angle subtracted from a right angle, 90°. For instance, if the angle is 30°, then its complement is 60°. Generally, for any angle t,
cos t = sin (90° – t).
Written in terms of radian measurement, this identity becomes
cos t = sin (∏/2 – t).
Right triangles and cosines
Consider a right triangle ABC with a right angle at C.
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A = 30°, (90° - A) = 60°
Consider the triangle PQR (drawing) with all three angles equal to 60°. By symmetry, all three sides are equal too (a more rigorous proof exists, but we skip it). Drop a line QS perpendicular to PR: it divides the big angle into two right-angled triangles with sharp angles of (30°, 60°), which is the kind we are interested in. By symmetry, the triangles are of equal size and shape ("congruent") and therefore (skipping another proof)
SR = (1/2) PR
In the notation of the drawing
a = (1/2) c
a/c = 1/2 = sin 30° = cos 60°
Continuing
sin2 30° = 1/4
But
sin2 30° + cos2 30° = 1
So
1/ 4 + cos2 30° = 1
Subtract 1/4 from both sides
cos2 30° = 3/4
cos 30° = SQRT(3)/ SQRT(4) = SQRT(3)/2 = 1.7320508/2
cos 30° = 0.8660254 = sin 60°
so you see they are equal.
Good question and Good luck
2006-08-28 12:11:26
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answer #1
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answered by sweetie 5
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If the 30 and 60 are in degrees, then they are equal. If they are in radians (which is the default), then sin 60 is larger.
2006-08-28 06:56:20
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answer #2
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answered by mathematician 7
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They are equal.
sin(a) = cos(90 - a), so if a = 30 deg
sin(60) = cos(90 - 60), sin(60) = cos(30)
perhaps you must know that
sin(60) = cos(30) = sqrt(3)/2
2006-08-28 06:44:34
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answer #3
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answered by Dimos F 4
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Equal.
2006-08-28 09:34:47
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answer #4
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answered by Sk8erboi83 3
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Equal.
2006-08-28 06:08:22
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answer #5
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answered by Kerk 2
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both values are equal
sin60 = cos [90-@]
@=theta
therefore
sin60=cos[90-60]
sin60=cos30
hence proved
2006-08-28 06:09:04
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answer #6
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answered by nave 1
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BOTH ARE EQUAL.
sin 60 =0.866
cos 30=0.866
2006-08-28 06:09:30
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answer #7
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answered by Anonymous
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in case you do degrees, they're both .886, and in case you do radians, this is sin60 = -.305 cos30= .154 in case you do not understand or you probably did not study radians in college, then purely flow with degrees and say they're both .886
2016-12-05 19:39:51
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answer #8
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answered by barras 3
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Both are the same No questions about that!!
2006-08-28 06:18:54
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answer #9
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answered by CodeRed 3
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Hey!
they are equal if they are in degrees
2006-08-31 08:40:55
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answer #10
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answered by Marla 3
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