mitchelsewbaran
Find an exact value.
cos 15°



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RadEn
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setting 15 = (4530)

RadEn
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then use the formula :
cos(AB) = cosAcosB + sinAsinB

RadEn
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here given A=45 and B=30 degrees

mitchelsewbaran
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cos 45cos30 +sin45cos30?

RadEn
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45 and 30 are the special angles.. u have to remember the values of sin and cos for angles 30 and 45 degrees

mitchelsewbaran
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ok. how do i solve from here?

RadEn
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u just put the values of them (sin45, sin 30, cos45, cos 30)

RadEn
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cos 45cos30 +sin45cos30
= ... (calculate it and simply)

mitchelsewbaran
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i got this

RadEn
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hmm.. what identity did u use ?
it should be : cos 45cos30 +sin45cos30
do u know the exactly value of sin30 ? sin45 ? cos30 ? cos45 ?

miley28
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just put the values cos45 =1/root 2 and cos 30= root3/2

miley28
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sin 45=1/root ovr2 and sin 30=1/2...the multiply and add

mitchelsewbaran
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1/root ovr2 or 1/ root 2?

miley28
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its the same thing...
