Two SHM’s are
x1=A1sinωt
x2=A2sin(ωt+π4)
Resultant amplitude is,
A=√(A12+A22+2A1A2cosπ4)
A= ⎷(A12+A22+2A1A2×1√2)
A=√(A12+A22+√2A1A2)