Correct option is A
Given,I=∫0πsin(mx)⋅cos(nx)dxWe know thatsinA⋅cosB=21[sin(A+B)+sin(A−B)]I=∫0π21[sin(mx+nx)+sin(mx−nx)]dxI=21∫0π[sin((m+n)x)+sin((m−n)x)]dxI=21∫0πsin((m+n)x)dx+21∫0πsin((m−n)x)dxI=−21[m−ncos((m−n)x)]0π+21[m+ncos((m+n)x)]0πI=−21[m−ncos((m−n)π)−m−ncos((m−n)⋅0)]+21[m+ncos((m+n)π)−m+ncos((m+n)⋅0)]I=0