A diffraction grating formed by parallel adjacent tracks on a CDROM

[help I have 12 hours]

Homework Statement

The parallel tracks on a CD-ROM reflect light just like a diffraction grating. Looking at a CD-ROM under white light, you observe a bright reflection of 475 nm blue light at 40.6° from normal incidence. The next bright blue reflection occurs at 77.2°.

Calculate the spacing between the CD-ROM tracks. Show your work here, and then enter your final numeric answer in the next answer box.

Relevant Equations

(d) sin(theta)=(wave length)*m

(d)sin(40.6)=(475*10^-9)(1)

d=730*10^-9 (m)

prof says answer is 1460*10^-9 (m) tho

 

[mfb]

I agree with your answer but something is weird in general. The 77.2 degree don't fit to the next band. 1.6 micrometers is the usual separation for a CD. 740 nm for a DVD.