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  • Thread starter kingboy
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  • #1
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Homework Statement



show that the expression 8 cos^2 x -6 sin x cos x +2 may be expressed in the form rcos (2x+α)+s ,and determine the value of the constants r,s and α.hence ,or otherwise, find the greatest and latest values of the expression as x varies.

Homework Equations



cos 2x=cos^2x-sin^2x ,sin2a=2 sinxcosx ,acos x-bsinx=rcos(x+α)

The Attempt at a Solution


8 cos^2 x -6 sin x cos x +2=8(cos 2x+sin^2x)+3(2 sinxcosx)+2=?????
 

Answers and Replies

  • #2
tiny-tim
Science Advisor
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hi kingboy! :smile:

(try using the X2 icon just above the Reply box :wink:)
cos 2x=cos^2x-sin^2x
learn all your trignonmetric identiies …

in this case, more useful would be cos2x = 2cos2x - 1 :wink:
 
  • #3
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in this case, more useful would be cos2x = 2cos2x - 1 :wink:
agreed :D
 

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