2cos(pi/4 + theta)cos(pi/4-theta)? (1 Viewer)

[kasser]

How would you simplify
2cos(pi/4 + theta)cos(pi/4-theta)?

The overall answer should be cos squared theta - sin squared theta = cos2theta

 

[anomalousdecay]

expand both sections.

You get 2[cos(pi/4)cos(theta)-sin(pi/4)sin(theta)][cos(pi/4)cos(theta) + sin(pi/4)sin(theta)]

Then you expand again then simplify and you get the final result.

 

[Parvee]

 

[Trebla]

How would you simplify
2cos(pi/4 + theta)cos(pi/4-theta)?

The overall answer should be cos squared theta - sin squared theta = cos2theta

Another approach is to note that



Let





and the result follows

 

[aDimitri]

Another approach is to note that



Let





and the result follows

This is what i was going to suggest
Products <--> Sums = winning

 

[Squar3root]

This is what i was going to suggest
Products <--> Sums = winning

not really in any of the hsc maths syllabus' but does come in handy