Let `a_(1) and a_(2)` be that amplitude of two light waves and `a_(1) and a_(2)` be their initial phases. The resultant amplitude due to supersition of two light waves is
A. `R= sqrt(a_(1)^(2)+a_(2)^(2)+2a_(1)a_(2))`
B. `R=a_(1)-a_(2)`
C. `R= sqrt(a_(1)^(2)+a_(2)^(2)+2a_(1)a_(2) cos (alpha-(1))alpha_(2)))`
D. `R=sqrt(a_(1)^(2)+a_(2)^(2)-2a_(1)-a_(2))`
