Sum, Difference, and Multiple-Angle Formulas · Easy problem

$\tfrac12\big[\sin 8x-\sin 2x\big]$

$\tfrac12\big[\sin 16x+\sin 2x\big]$

$\tfrac12\big[\sin 8x+\sin 2x\big]$

$\tfrac12\big[\sin 8x+\sin 3x\big]$