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+2 votes
56.1k views
in Mathematics by (54.8k points)

The value of cos3(π/8).cos(3π/8) + sin3(π/8).sin(3π/8) is:

(1) 1/4

(2) 1/2

(3) 1/22

(4) 1/2

2 Answers

+2 votes
by (58.3k points)
selected by
 
Best answer

Answer is (3)

by (10 points)
How did you write sin in place of cos see question you have swapped them . It's not possible to change question . And if you have a valid reason then please write it .
by (44.0k points)
edited by
cos(3π/8) = cos( π/2 - π/8) = sin(π/8)
and sin (3π/8) = sin (π/2 - π/8) = cos(π/8)
Therefore, we used cos in place of sin.
+1 vote
by (52.5k points)

Answer is (3)

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