Find the exact value of cos(135) and sin(135).

To find the exact value of cos(135), you need the following formula: cos(a+b) = cos a • cos b - sin a • sin b So in this case, it would be: cos (135) = cos ( 45 + 90) = cos 45 • cos 90 - sin 45 • sin 90 = √(2)/2 · 0 - √(2)/2 · 1 = 0 - (√2)/2 = - (√2)/2.

To find the exact value of sin(135), you need the following formula: sin (a+b) = sin a • cos b - cos a + sin b So in this case, it would be sin (135) = sin (90 + 45) = sin 90 • cos 45 + cos 90 • sin 45 = (1 ·(√2)/2) + (0 · (√2)/2) = (√2)/2).
 
cos (135)= - (√2)/2  

sin (135) = (√2)/2