9)
Cos 5π/8·Cos3π/8+Sin5π/8·Sin3π/8=
=Cos(5π/8-3π/8)=Cos2π/8=Cosπ/4=Cos45°=√2
2
10)
Sin63°·Cos27°+Cos63°·Sin27°=Sin(63°+27°)=Sin90°=1
11)
2Sin15°·Cos15°=Sin2·15°=Sin30°=1/2
12)
2Sin75°·Cos75°=Sin2·75°=Sin150°=Sin(180°-30°)=Sin30°=1/2
13)
2Sin22,5·Cos22,5=Sin2·22,5=Sin50°=Sin(90°-30°)=Cos30°=√3/2