Simplify the expression by using a sum or difference identity.cos(12k) cos (9k) - sin(12k) sin (9k)
A. sin(21k)
B. sin(3k)
C. cos(21k)
D. cos(3k)
Answer: C
Mathematics
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Find the volume of the solid generated by revolving the region bounded by the given lines and curves about the 
. y = 
, y = 5, x = 0
A. 
?
B. 
?
C. 
?
D. 50?
Mathematics
Solve the problem.If one earthquake is 398,107 times as intense as another, what is the difference in the Richter scale readings of the two earthquakes?
A. 4.6 B. 5.6 C. 0.56 D. 12.9
Mathematics
Write the number in standard form.It takes approximately 1.578 × 10-5 miles to equal one inch.
A. 0.000001578 B. 157,800 C. 0.00001578 D. 0.0001578
Mathematics
Find the focus and directrix of the parabola.x2 = 8y
A. F: (2, 0); D: x = 2 B. F: (0, 2); D: y = -2 C. F: (0, -2); D: x = - 2 D. F: (2, 0); D: y = 2
Mathematics