Help with double angle formulas

[Sayf44]

Use double angle formulas to find the exact value of:

sin(pie/8)

Can you please show detailed working out, particularly for the parts where you apply double angle formulas. I also have no idea how to start this question.

[Billion]

Sorry I can't answer your question, however hopefully someone can answer mine as well (instead of making a new thread).

How does cos(100 degrees) = 2cos²(50 degrees)-1

Thanks in advance.

[Sayf44]

remember the formula cos(2x)= cos^2(x) - 1

cos(100) can also be written as cos(2(50)) and x=50

therefore: cos(2(50))= cos^2(50) - 1

[Billion]

remember the formula cos(2x)= cos^2(x) - 1

cos(100) can also be written as cos(2(50)) and x=50

therefore: cos(2(50))= cos^2(50) - 1

LOL forgot about that.
Cheers mate.

[Sayf44]

Np

Dw guys i figured it out.