2007-11-04 01:32:31 · 8 answers · asked by Jenny D 1 in Science & Mathematics ➔ Mathematics
1. find the reference angle (the angle formed by the terminal ray of the angle and the x-axis...always an acute angle)
in this case it's 45 degrees
2. the angle terminates in quadrant three, so the cosine value must be negative.
3. so we are looking for the -cos 45
4. the answer is -radical two over two
2007-11-04 01:42:40 · answer #1 · answered by imalava 2 · 0⤊ 0⤋
225° is in 4 th quadrant
cos 225° = - cos 45° = - 1 / √2 = - √2 / 2
2007-11-04 03:51:35 · answer #2 · answered by Como 7 · 0⤊ 1⤋
Cos 225 = Cos90 + Cos90 + Cos45
Therefore,
Cos90 = 0, Cos45 = 1/ root 2
so,
= 0 + 0 + 1/ root 2
= 1/ root 2 now On rationalizing the denominator,
= root2/ 4.
= 0.35355339059
2007-11-04 02:12:04 · answer #3 · answered by Anonymous · 0⤊ 0⤋
Interesting: -0.862303608
according to Excel 2007
Function cos(255)
http://spreadsheets.about.com/od/excelfunctions/qt/070829_cos.htm
2007-11-04 01:44:38 · answer #4 · answered by loclemons 3 · 0⤊ 0⤋
cos(225) = cos(180+ 45)
=>cos180 cos45 - sin180 sin45
=>-1(1/sqrt(2)) - 0 = -1/sqrt(2) = -0.707
2007-11-04 01:48:55 · answer #5 · answered by mohanrao d 7 · 0⤊ 0⤋
225 degrees = 5pi/4
5pi/4 is one of our known values on the unit circle.
cos(5pi/4) = -sqrt(2)/2
2007-11-04 01:38:39 · answer #6 · answered by Puggy 7 · 0⤊ 0⤋
In Excel use function RADIANS(225) and get 3.92699.
Then use function COS(3.92699) and get the result.
-
2007-11-04 01:41:17 · answer #7 · answered by oregfiu 7 · 0⤊ 0⤋
-.7071067812 roughly, according to my calculator.
the exact value is -1/2 * √2
2007-11-04 01:36:12 · answer #8 · answered by I Need Help 4 · 0⤊ 0⤋