7 + k/3= 18 please help me answer this question it’s due tomorrow
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It's a value you should probably memorize:
You can derive it using some trigonometric identities, other known values of cosine, and properties of the cosine function. For example, using the double angle identity for cosine:
If , then
and you probably know that , so
When we take the square root, we should take the positive root because whenever
: