Science

Math

Humanities

... and beyond

Socratic Meta
Featured Answers

Topics

Question #ea04c

1 Answer

Mar 21, 2017

#cos (pi/7 )cos ((4pi)/21) - sin (pi/7) sin ((4pi)/21)#

#=cos (pi/7 +(4pi)/21) #

#=cos( (3pi +4pi)/21) #

#=cos( (7pi)/21) #

#=cos( (pi)/3) =1/2#

Related questions

See all questions in Trigonometric Functions of Any Angle

Impact of this question

1023 views around the world

You can reuse this answer
Creative Commons License