# Trigonometry: Product Identities (DTube)

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In this video I go over the trig product identities and provide a simple proof for them. The identities I cover are listed below:

sin(x)cos(y) = 1/2 [sin(x+y) + sin(x-y)]
cos(x)cos(y) = 1/2[cos(x+y) + cos(x-y)]
sin(x)sin(y) = 1/2[cos(x-y) - cos(x+y)]

In proving the above identities I make use of the identities which I covered in my earlier video (see the related videos below), specifically the identities for sin(x+/-y) and cos(x+/-y).

View Video Notes on Steemit: https://steemit.com/mathematics/@mes/trigonometry-product-identities

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