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Mathematics 21 Online
OpenStudy (brydenwright):

Write the expression as either the sine, cosine, or tangent of a single angle. cos(pi/5)cos(pi/7)+sin(pi/5)sin(pi/7)

OpenStudy (evoker):

That's the cosine difference identity.

jhonyy9 (jhonyy9):

yes sure @Evoker this wan being cos(pi/5 -pi/7) so will be cos(2pi/35) do you thought it hence ?

OpenStudy (evoker):

Yes I agree

OpenStudy (pythagoras123):

\[\cos(A-B)=cosAcosB+sinAsinB \]

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