The x-intercepts of a function is determined by replacing y or f(x) to zero since this is the point of x where it crosses the x-axis (y=0). In this case, for f(x)= sin (x + π/4) , we substitute 0 = sin (x + π/4). sin^-1 of zero is also zero and pi. hence
x + π/4 = 0
x = -π/4
x + π/4 = π
x = 3π/4
