Trigo Identities

Y_Shun SG

Any idea/guide into solving it?

I suck in it...zzz always cannot prove >_>.

eagle SG

when in doubt, always resolve into just sine and cosine.
Work halfways from both sides
Join it up

Almost 80+% of the time can solve by this brute force method

kristovorus SG

have u had ur identities memorised by heart? while they do provide certain identities, its essential to memorise all ur identities so u can recognize when and where to change the identities and more importantly, when NOT to change the identity when doing so would be irrelevant

^tamago^ SG

Sometimes changing them to tan and sec could be helpful too.
Some questions involve simple algebraic identities a²-b²=(a-b)(a+b)
Some may involve multiple angle, which we all hate most probably Laughing

But eagle is right. Work halfways, or work from RHS if LHS seems impossible.

To proof is to find a mathematical "pathway" from one to another and that's all you need.

tanjun SG

Just to addon, if u r stuck from working for example from RHS. Don't just give up. Start working from the LHS writing your ans in a rough paper and stop at the point when u obtain the same term as from your RHS. Then, play cheat by reversing the process.

It is easy to simplify and cancel out common term but is difficult to add term.

eagle SG

Oh ya, I forgot to mention

Usually start from the side that looks more complicated

wishboy SG

trigo identity actually got only 2 (up to sec 3 lvl)
which is "tan x = sin x/cos x" , and "sin² x + cos² x = 1"
other ones like "tan² x + 1 = sec² x" are derived from "sin² x + cos² x = 1"