Use an addition or subtraction formula to write the expression as a
trigonometric function of one number:
cos 3 π 7 cos 2 π 21 + sin 3 π 7 sin 2 π 21 = cos π A = B 2 \displaystyle {\cos{{\frac{{{3}\pi}}{{{7}}}}}}{\cos{{\frac{{{2}\pi}}{{{21}}}}}}+{\sin{{\frac{{{3}\pi}}{{{7}}}}}}{\sin{{\frac{{{2}\pi}}{{{21}}}}}}={\cos{{\frac{{\pi}}{{{A}}}}}}={\frac{{{B}}}{{{2}}}} cos 7 3 π cos 21 2 π + sin 7 3 π sin 21 2 π = cos A π = 2 B .
A = \displaystyle {A}= A = Preview Question 6 Part 1 of 2 ,
B = \displaystyle {B}= B = Preview Question 6 Part 2 of 2 .
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Enter your answer as a number (like 5, -3, 2.2172) or as a calculation (like 5/3, 2^3, 5+4)
Enter your answer as a number (like 5, -3, 2.2172) or as a calculation (like 5/3, 2^3, 5+4)