Different ways to say 'You're welcome' to sound like a native speaker

Name each of the following triangles in two different ways: (you may judge the nature of the angle by observation)

Two speakers separeted by some distance emit sound of the same frequency. At some point P the intensity due to each speaker separately is I_(o) . The path difference from P to one of the speakers is (1)/(2) lambda greater than that from P to the other speaker. What is the intensity at P if (a) the speakers are coherent and in phase, (b) the speakers are incoherent, and (c ) the speakers are coherent but have a phase different of 180^(@) ?

Two speakers S1 and S2 are a driven by same source. You walk along a line l that is perpendicular bisector of the line joining the two speakers and record the intensity at different points. Then you walk along a line m that is parallel to the line joining the speakers and record the intensity of sound at various points. On which path you observe the loudness to alternate between faint and loud? Explain.