Hint for the second mandatory assignment

To get condition (5) you need to (among other things) use the Taylor series expansion of the sine function. Note that there is a way to simplify condition (5) by either multiplying out the brackets and argue why you can drop the higher order term, or by just considering the Taylor series expansion of the sine function squared. If you would rather show this simpler condition, and later test it in exercise (g), then that would be fine.