Find cos(1217π) exactly using an angle addition or subtraction formula.[Hint: This diagram of special trigonometry. values may help.].Choose 1 answer:(A) 42−6(B) 4−2−6(C) 4−2+6(D) 42+6
Q. Find cos(1217π) exactly using an angle addition or subtraction formula.[Hint: This diagram of special trigonometry. values may help.].Choose 1 answer:(A) 42−6(B) 4−2−6(C) 4−2+6(D) 42+6
Expressing (1217π) as a sum or difference: We need to express (1217π) as a sum or difference of angles for which we know the cosine values exactly. The angles we can use are typically multiples of 6π, 4π, or 3π because these correspond to special angles in the unit circle (30∘, 45∘, and 60∘ respectively).
Using the angle addition formula for cosine: We can write (1217π) as the sum of (124π) and (1213π). Since (124π) simplifies to (3π) and (1213π) simplifies to (4π+6π), we can use the angle addition formula for cosine to find the exact value of cos(1217π).
Finding the cosine and sine values: The angle addition formula for cosine is cos(α+β)=cos(α)cos(β)−sin(α)sin(β). We will use α=3π and β=4π+6π.
Finding the cosine and sine of (π/4+π/6): First, we need to find the cosine and sine values for π/3, π/4, and π/6. From the unit circle, we know that:cos(π/3)=1/2,sin(π/3)=3/2,cos(π/4)=2/2,sin(π/4)=2/2,cos(π/6)=3/2,sin(π/6)=1/2.
Calculating cos(1217π) using the angle addition formula: Now we need to find the cosine and sine of (4π+6π) using the angle addition formulas for cosine and sine:cos(4π+6π)=cos(4π)cos(6π)−sin(4π)sin(6π),sin(4π+6π)=sin(4π)cos(6π)+cos(4π)sin(6π).
Substituting the known values into the formula: Substitute the known values into the formulas:cos(4π+6π)=(22)(23)−(22)(21)=(46)−(42),sin(4π+6π)=(22)(23)+(22)(21)=(46)+(42).
Performing the multiplication: Now we can find cos(1217π) using the angle addition formula with α=3π and β=4π+6π:cos(1217π)=cos(3π)cos(4π+6π)−sin(3π)sin(4π+6π).
Simplifying the expression: Substitute the known values into the formula: \cos\left(\frac{\(17\)\pi}{\(12\)}\right) = \left(\frac{\(1\)}{\(2\)}\right)\left(\frac{\sqrt{\(6\)}}{\(4\)} - \frac{\sqrt{\(2\)}}{\(4\)}\right) - \left(\frac{\sqrt{\(3\)}}{\(2\)}\right)\left(\frac{\sqrt{\(6\)}}{\(4\)} + \frac{\sqrt{\(2\)}}{\(4\)}\right).
Simplifying the expression: Substitute the known values into the formula: \(\newlinecos(1217π)=(21)(46−42)−(23)(46+42).Perform the multiplication: \cos\left(\frac{17\pi}{12}\right) = \left(\frac{1}{2}\right)\left(\frac{\sqrt{6}}{4}\right) - \left(\frac{1}{2}\right)\left(\frac{\sqrt{2}}{4}\right) - \left(\frac{\sqrt{3}}{2}\right)\left(\frac{\sqrt{6}}{4}\right) - \left(\frac{\sqrt{3}}{2}\right)\left(\frac{\sqrt{2}}{4}\right),\(\newline\\cos\left(\frac{17\pi}{12}\right) = \frac{\sqrt{6}}{8} - \frac{\sqrt{2}}{8} - \frac{\sqrt{18}}{8} - \frac{\sqrt{6}}{8}\).
Simplifying the expression: Substitute the known values into the formula: \(\cos\left(\frac{17\pi}{12}\right) = \left(\frac{1}{2}\right)\left(\frac{\sqrt{6}}{4} - \frac{\sqrt{2}}{4}\right) - \left(\frac{\sqrt{3}}{2}\right)\left(\frac{\sqrt{6}}{4} + \frac{\sqrt{2}}{4}\right)\). Perform the multiplication: \(\cos\left(\frac{17\pi}{12}\right) = \left(\frac{1}{2}\right)\left(\frac{\sqrt{6}}{4}\right) - \left(\frac{1}{2}\right)\left(\frac{\sqrt{2}}{4}\right) - \left(\frac{\sqrt{3}}{2}\right)\left(\frac{\sqrt{6}}{4}\right) - \left(\frac{\sqrt{3}}{2}\right)\left(\frac{\sqrt{2}}{4}\right), \)\cos\left(\frac{\(17\)\pi}{\(12\)}\right) = \frac{\sqrt{\(6\)}}{\(8\)} - \frac{\sqrt{\(2\)}}{\(8\)} - \frac{\sqrt{\(18\)}}{\(8\)} - \frac{\sqrt{\(6\)}}{\(8\)}\(. Simplify the expression: \)\cos\left(\frac{\(17\)\pi}{\(12\)}\right) = \frac{\sqrt{\(6\)}}{\(8\)} - \frac{\sqrt{\(2\)}}{\(8\)} - \frac{\(3\)\sqrt{\(2\)}}{\(8\)} - \frac{\sqrt{\(6\)}}{\(8\)}, \(\cos\left(\frac{17\pi}{12}\right) = - \frac{\sqrt{2}}{8} - \frac{3\sqrt{2}}{8}, \)\cos\left(\frac{\(17\)\pi}{\(12\)}\right) = - \frac{\(4\)\sqrt{\(2\)}}{\(8\)}, \cos\left(\frac{17\pi}{12}\right) = - \frac{\sqrt{2}}{2}.