3∗sin(
12
13pi
)∗cos(
12
13pi
)=
2
3
∗2∗sin(
12
13pi
)∗cos(
12
13pi
)=
=\frac{3}{2}*sin( \frac{2*13pi}{12}) = \frac{3}{2}*sin( \frac{13pi}{6}) = \frac{3}{2}*sin(2pi+ \frac{pi}{6}) = \frac{3}{2}*sin( \frac{pi}{6}) = \frac{3}{2}*\frac{1}{2}==
2
3
∗sin(
12
2∗13pi
)=
2
3
∗sin(
6
13pi
)=
2
3
∗sin(2pi+
6
pi
)=
2
3
∗sin(
6
pi
)=
2
3
∗
2
1
=
=\frac{3}{2}*\frac{1}{2} = \frac{3}{4}=
2
3
∗
2
1
=
4
3
