Another trig question

**ceroseven** · February 3rd 2010, 10:41 PM

Value of cos65°cos12°+sin65° sin12°

-The Answer must be in either sin or cos and must be followed with a degree (i.e. cos88°)

1.6

**VonNemo19** · February 3rd 2010, 11:00 PM

Originally Posted by ceroseven

Value of cos65°cos12°+sin65° sin12°

-The Answer must be in either sin or cos and must be followed with a degree (i.e. cos88°)

1.6

You want the seccend sum or difference identity, here

Table of Trigonometric Identities

**ceroseven** · February 3rd 2010, 11:15 PM

How would this be substituted in the equation?

**VonNemo19** · February 4th 2010, 08:31 PM

Originally Posted by ceroseven

How would this be substituted in the equation?

Let $u=65^\circ$ and let $v=12^\circ$ , then your problem reduces to

$\cos65^\circ\cos12^\circ+\sin65^\circ\sin12^\circ= \cos(65^\circ-12^\circ)=\cos53^\circ$

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