These problems are best solved geometrically using phasors (vectors). The general funda is that Asin(t+) can be represented by Aei, that is a vector of magnitude A at an angle with +X axis. A cost is a vector of magnitude A along the +Y axis. (A/2)cos(t+/4) is a vector of magnitude A/2 making an angle /4 + /2 with X axis. (A/4)cos(t+) is a vector of magnitude A/4 along the negative Y axis. (A/8)cos(t+3/2) is a vector of magnitude A/8 along +X axis. Add these vectors. Now the answer will be in the form Asin(t+) The resultant magnitude is the A. The angle the resultant makes with the +X axis is the .