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 2 years ago
Evaluate sin (840) without using a calulator.
My answer is (1/2) but i'm not too good with these so can someone please check it? Thanks:)
 2 years ago
Evaluate sin (840) without using a calulator. My answer is (1/2) but i'm not too good with these so can someone please check it? Thanks:)

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jim_thompson5910
 2 years ago
Best ResponseYou've already chosen the best response.0sin(840) = sin(840) .... since sine is an odd function sin(840) = sin(480) .... 480 and 840 are coterminal angles sin(840) = sin(120) ... 480 and 120 are coterminal angles sin(840) = sqrt(3)/2 ... use the unit circle (link given below) to find this value So the answer is sin(840) = sqrt(3)/2 Unit Circle: http://www.math.ucsd.edu/~jarmel/math4c/Unit_Circle_Angles.png

greeneyes<3
 2 years ago
Best ResponseYou've already chosen the best response.0Thank you! I figured it out my mistake and then you posted this! I have memorize all the unit circle... :( Thank you so much anyways! Is the answer to sec (15 pi/4) = sqrt 2/2 ?

jim_thompson5910
 2 years ago
Best ResponseYou've already chosen the best response.0sec(15pi/4) = 1/cos(15pi/4) sec(15pi/4) = 1/cos(15pi/4) ... Note: cosine is an even function sec(15pi/4) = 1/cos(pi/4) ... 15pi/4 is coterminal with pi/4 sec(15pi/4) = 1/cos(pi/4) sec(15pi/4) = 1/(sqrt(2)/2) ... Use the unit circle here sec(15pi/4) = 1*(2/sqrt(2)) sec(15pi/4) = 2/sqrt(2) sec(15pi/4) = (2/sqrt(2))*(sqrt(2)/sqrt(2)) ... Rationalizing the denominator sec(15pi/4) = (2*sqrt(2))/(sqrt(2)*sqrt(2)) sec(15pi/4) = (2*sqrt(2))/(sqrt(2*2)) sec(15pi/4) = (2*sqrt(2))/(sqrt(4)) sec(15pi/4) = (2*sqrt(2))/(2) sec(15pi/4) = sqrt(2) So the answer is sec(15pi/4) = sqrt(2)

phi
 2 years ago
Best ResponseYou've already chosen the best response.0Thank you so much anyways! Is the answer to sec (15 pi/4) = sqrt 2/2 ? You found the cos(15 pi/4) . Do you know how you went wrong?

phi
 2 years ago
Best ResponseYou've already chosen the best response.0btw, for sin(840), I would keep adding 360 until I get to a number I like 840+ 2*360= 120 or 120+360= 240 of course 120 and 240 are the same angle.
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