Hello
sin ..... | 0° |30°|45°|60°|90°|
...........| 0...| 1..| 2..| 3..| 4..| write numbers
...........| 0...| 1..|√2.| √3 | 2..| take root square
...........| 0...|1/2|√2/2|√3/2|1| divide by 2
...........| 0...|1/2|√2/2|√3/2|1| .....
cos.....| 90°|60°|45°|30°| 0°|
sin (75°)
=sin(30°+45°)=sin 30°*cos 45° +cos 30°*sin 45°
.................... =1/2*√2/2 + √3/2*√2/2
.................... = √2(1+√3)/4
cos 75°
=cos(30°+45°)=cos 30°*cos 45°-sin 30°*cos 45°
=√3/2*√2/2-1/2*√2/2
=√6/4-√2/4=√2/4*(√3 -1 )