# Sum and difference identities

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Find the coordinates of P(Ï€/12)

x = (1+âˆš3)/(2âˆš2)

To find the y-coordinate you use the identity:

sin(Î±- Î²) = (sinÎ±)(cosÎ²) (cosÎ±)(sinÎ²)

Why do we use this identity? eg, why don't we use

sin(Î± + Î²) = (sinÎ±)(cosÎ²) + (cosÎ±)(sinÎ²) ??

https://brainmass.com/math/complex-analysis/sum-difference-identities-28527

#### Solution Preview

To find y_coordinate, we can use

y=sqrt(1-x^2)=(-1+âˆš3)/(2âˆš2)

If we use identities, then we let β=Ï€/12 and Î±=Ï€/6, then ...

#### Solution Summary

This solution shows how to use the difference identity to find coordinates.

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