How do you simplify #cos2ucos7u-sin2usin7u#?

1 Answer
Anthony X
Oct 23, 2016

If you learned the sum and difference formulas for trigonometric identities, you know that

#cos(a+b) = cosacosb - sinasinb#

Therefore, if we have

#cos2ucos7u - sin2usin7u#, we see that #2u# can be plugged in as #a# and #7u# can be plugged in as #b#

Therefore, we have that this equals #cos(2u+7u)# or #cos(9u)#

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