Question

@kc_kennylau why do you subtract and then add the sin^2 t ?

Answer 1

Welcome to Open Study! Having any questions or problems? Just ask me or anyone with a purple A next to their username!

Answer 2

ok thx! @sammixboo

Answer 3

What was the question?

Answer 4

cos^4t - sin^4t = 1-2sin^2t you answered this question asked by @queenbeedoe

Answer 5

\[\cos^4t-\sin^4t\]\[=(\cos^2t+\sin^2t)(\cos^2t-\sin^2t)\]\[=\cos^2t-\sin^2t\]\[=\cos^2t+\sin^2t-2\sin^2t\]\[=1-2\sin^2t\]

Answer 6

In order to form \(\cos^2t+\sin^2t\).

Answer 7

Oh i see but when you were solving for @queenbeedoe you wrote the third step like this:
= cos^2t + (sin^2t - sin^2t) - sin^2t so i was confused.

Answer 8

OHHHHHH i understand it now!!! nevermind im so sorry im so stupid. You wrote it like that to get a "1" for 1- 2sin^2t am i correct?

Answer 9

Yep :)