Some Trig Questions I Need Help With (1 Viewer)

[kevinsta]

How would i find the exact value of cos(-225) and Sin(315), can you please show me how you got to it, i used to know this but when i was revising i was completely lost.

 

[aDimitri]

cos(-225) = cos(360-225) = cos(135) = -cos(45) = -1/sqrt(2)
sin(315) = sin(360-45) = -sin(45) = -1/sqrt(2)

 

[kevinsta]

how about cos(-150)

 

[bongoli]

if it's negative, just do it opposite of how you normally do it. Draw up your quadrants and then draw 150 degrees in the opposite direction. Find out what quadrant it is in... ASTC > (All(1st), Sine(2nd), Tan(3rd), Cosine(4th) then do 360- your angle which would be 210 degrees. This means it is in the 3rd quadrant. Cosine is negative in this quadrant and it follows the rule of 180+theta.

210 = 180 + theta
Therefore it is -cos(30) and this equates to -sqrt(3)/2

follow the same train of thought for these kind of equations, gl

 

[kevinsta]

if it's negative, just do it opposite of how you normally do it. Draw up your quadrants and then draw 150 degrees in the opposite direction. Find out what quadrant it is in... ASTC > (All(1st), Sine(2nd), Tan(3rd), Cosine(4th) then do 360- your angle which would be 210 degrees. This means it is in the 3rd quadrant. Cosine is negative in this quadrant and it follows the rule of 180+theta.

210 = 180 + theta
Therefore it is -cos(30) and this equates to -sqrt(3)/2


follow the same train of thought for these kind of equations, gl

Omg man thanks so much i fully understand it now have a nice day