I have a problem, that i simply cannot get the right answer for. I have tried using the principles of Double-Angle Formulas and Sum and Difference Formulas but i am not sure if i am doing it correctly. I was hoping someone could walk me through this so that i know what to do and will be able to repeat this for other questions of this type

lim x-->a $\displaystyle [sin(a + 2x) - 2sin(a + x) + sin (a)]/x^2$