double slit final equations

content/physics/harmonic-motion.md

@@ -514,4 +514,14 @@ Where:
   - $ D $ = distance from the slits to the screen
   - $ d $ = distance between the two slits
 
+## Final equations
 
+Time to combine everything together. We'll continue to use the variable definitions from above, but include $y_m$, or the distance between the center, $m=0$ and some bright fringe of order $m$. When calculating, it can also be assumed that (for small angles) $\sin\theta\approx\theta$.
+
+$$
+\box{d\sin\theta=m\lambda}
+$$
+
+$$
+\box{y_md=Dm\lambda}
+$$