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chapter ten section one
in chapter we are not using calculators so if you do not know your trig chart you will fail!

For section one you only have memorize two formulas.

first formula: cosine (alpha plus or minus beta)= cosine alpha cosine beta minus or plus sine alpha sine beta

second formula:sine (alpha plus or minus beta)= sine alpha cosine beta minus or plus cosine alpha sine beta

example

find the exact value of cosine 75 degrees

alpha= 45
beta= 30

cosine(45+30)= cosine 45 cosine 30- sine45 sine30

cosine(75) =(square root of 2 divided by 2)(square root 3 divided by 2)-(square root of 2 divided by 2)(one divided by two)

Do not simplify the problem because need to have the same denominatior

cosine(75)=(square root of six divided by four)(square root of two divided by four)

and you leave as that for your answer