10-1

10-1 has plenty of formulas.

Formulas:

1. Cos(alpha+-beta)=CosalphaCosbeta-+SinalphaSinbeta
2. Sin(alpha+-beta)=SinalphaCosbeta+-CosalphaSinbeta
3. Sinx+Siny=2Sin x+y/2Cos x-y/2
4. Sinx-Siny=2Cos x+y/2Sin x-y/2
5. Cosx+Cosy=2Cos x+y/2Cos x-y/2
6. Cosx-Cosy=-2Sin x+y/2Sin x-y/2

Example 1: Find the exact value of sin150 degrees.

• Step one: Look on the trig chart and see if any of the degrees add up to give you 150 degrees. 90+60=150
  
• Step two: Place 90 and 60 in the formula, sin(alpha+-beta)=sinalphacosbeta+-cosalphasinbeta
• Step three: Sin(90+60)=Sin90Cos60+Cos90Sin60

And after that just solve it and get the exact value.

Amber :)