# Sum and difference identities

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Find the coordinates of P(π/12)

x = (1+√3)/(2√2)

To find the y-coordinate you use the identity:

sin(α- β) = (sinα)(cosβ) (cosα)(sinβ)

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

sin(α + β) = (sinα)(cosβ) + (cosα)(sinβ) ??

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##### Solution Summary

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

##### Solution Preview

To find y_coordinate, we can use

y=sqrt(1-x^2)=(-1+√3)/(2√2)

If we use identities, then we let β=π/12 and α=π/6, then ...

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