Proving. Sec 4 A Maths Help

galaxy_twirls SG

Hi everyone.

I need help on an A Maths question which I'm super stuck at and desperately need help. T_T

How do you prove:

4 sin^2 (x) - 7sin x cos x - 5 cos^3 (x) = -2

I have tried applying trig identities but I can't seem to get anything... From the above, it means that the sines and cosines have to cancel out to yield a constant right? Can anyone guide me to see the pattern in the above? Thanks! :D

wee_ws SG

Hi,

Don't worry, this question is problematic in the first place.

It is easy to provide a counterexample (let x = 0) to show that the equation does not hold.

Thanks.

Cheers,
Wen Shih

galaxy_twirls SG

Hi Wen Shih,

Thank you for you help! Oh dear, why didn't I check it? >< My apologies for posting this. :X Thanks for your guidance again! :D

Regards,

galaxy_twirls