If θ is an acute angle and sin θ = (2√7) / 7, use the identity sin²θ + cos²θ = 1 to find cos θ.

In Exercises 21–28, convert each angle in radians to degrees. -3𝜋
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주요 개념
Radian Measure
Degree Measure
Conversion between Radians and Degrees
In Exercises 28–29, find a cofunction with the same value as the given expression. sin 70°
In Exercises 25–32, the unit circle has been divided into eight equal arcs, corresponding to t-values of 0, 𝜋, 𝜋, 3𝜋, 𝜋, 5𝜋, 3𝜋, 7𝜋, and 2𝜋. 4 2 4 4 2 4 a. Use the (x,y) coordinates in the figure to find the value of the trigonometric function. b. Use periodic properties and your answer from part (a) to find the value of the same trigonometric function at the indicated real number.
cos 9𝜋/2
In Exercises 23–34, find the exact value of each of the remaining trigonometric functions of θ. cos θ = 8/17, 270° < θ < 360°
In Exercises 25–30, use an identity to find the value of each expression. Do not use a calculator. sin² 𝜋 + cos² 𝜋 10 10
In Exercises 25–32, the unit circle has been divided into eight equal arcs, corresponding to t-values of
0, 𝜋, 𝜋, 3𝜋, 𝜋, 5𝜋, 3𝜋, 7𝜋, and 2𝜋.
4 2 4 4 2 4
a. Use the (x,y) coordinates in the figure to find the value of the trigonometric function.
cos 3𝜋/4
