Giải ptsinx=a 2sinx(45°+3x)+1=0

$$\eqalign{ & 2\sin \left( {{{45}^0} + 3x} \right) + 1 = 0 \cr & \Leftrightarrow \sin \left( {{{45}^0} + 3x} \right) = - {1 \over 2} \cr & \Leftrightarrow \left[ \matrix{ {45^0} + 3x = - {30^0} + k{360^0} \hfill \cr {45^0} + 3x = {180^0} + {30^0} + k{360^0} \hfill \cr} \right. \cr & \Leftrightarrow \left[ \matrix{ 3x = - {75^0} + k{360^0} \hfill \cr 3x = {165^0} + k{360^0} \hfill \cr} \right. \cr & \Leftrightarrow \left[ \matrix{ x = - {25^0} + k{120^0} \hfill \cr x = {55^0} + k{120^0} \hfill \cr} \right.\,\,\left( {k \in Z} \right) \cr}$$