You just draw 2 right-angled triangles
1.... the angles =45,45,90
the opposite side of 45=1
the opposite side of 90=√2
you can understand here cos 45=sin45=1/√2
2.....the angles =30,60,90
the opposite side of 30=1
the opposite side of 60=√3
the opposite side of 90=2
cos 30=sin 60= 1/2
sin 90=1
