use double-angle identities to solve [0,2pi]
-4sinx.cosx = 0.5

Question

use double-angle identities to solve [0,2pi]
-4sinx.cosx = 0.5

anonymous · Answer

i'm not so sure it is right or not

anonymous · Answer

but when I put it in the answer box, it tells me wrong :(

tkhunny · Answer

It's pretty subtle,  but there is one tiny thing.  You may have used the rounded values from the first two answers, and a rounded value of $\pi$ to create the second two answers.

$\theta_{1} = \dfrac{\pi - asin(-0.25)}{2} = 1.697136454365935946$
Rounded 1.6971

$\theta_{2} = \dfrac{2\pi + asin(-0.25)}{2} = 3.0152525260187539117$
Rounded 3.0153

$\theta_{3} = \dfrac{\pi - asin(-0.25)}{2} + \pi = 4.8387291079557291844$
Rounded 4.8387

$\theta_{4} = \dfrac{2\pi + asin(-0.25)}{2} + \pi = 6.1568451796085471502$
Rounded 6.1568

Round later and never use a short rounded number to create subsequent values.

tkhunny · Answer

Note: Amazingly clear and legible work!!  Keep that up!