Trigonometry Examples

Find the Exact Value cos((5pi)/8)
Step 1
Rewrite as an angle where the values of the six trigonometric functions are known divided by .
Step 2
Apply the cosine half-angle identity .
Step 3
Change the to because cosine is negative in the second quadrant.
Step 4
Simplify .
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Step 4.1
Apply the reference angle by finding the angle with equivalent trig values in the first quadrant. Make the expression negative because cosine is negative in the third quadrant.
Step 4.2
The exact value of is .
Step 4.3
Write as a fraction with a common denominator.
Step 4.4
Combine the numerators over the common denominator.
Step 4.5
Multiply the numerator by the reciprocal of the denominator.
Step 4.6
Multiply .
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Step 4.6.1
Multiply by .
Step 4.6.2
Multiply by .
Step 4.7
Rewrite as .
Step 4.8
Simplify the denominator.
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Step 4.8.1
Rewrite as .
Step 4.8.2
Pull terms out from under the radical, assuming positive real numbers.
Step 5
The result can be shown in multiple forms.
Exact Form:
Decimal Form: