# Algebra 2 Honors

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Find the exact value by using an appropriate sum or difference identity.

cos(165) degrees

• Algebra 2 Honors -

For these type of questions, you must split up your given angles into a sum or a difference of angles whose trig ratios you know

e.g. 165 = 120+45
then cos(165)
= cos(120+45)
= cos120cos45 - sin120sin45

you should know both sin45 and cos45
for sin120,
sin120 = sin60
cos120 = -cos60

take it from here

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