Given here, I2I1=41 or I2=4I1
Maximum intensity is Imax=(I1+I2)2=I1+4I1+2I14I1=9I1
Minimum intensity is Imin=(I1−I2)2=I1+4I1−2I14I1=I1
The ratio of Imax−IminImax+Imin is
9I1−I19I1+I1=810=45=β+32α+1
α=2β=1
∴βα=12=2