which is satisfied when !2 ¼ g=l þ 2s=m, the second normal mode frequency.
Inserting the value !2 ¼ g=l in the pair of equations gives A ¼ B (the ‘in phase’
condition), whilst !2 ¼ g=l þ 2s=m gives A ¼ B (the antiphase conditon).
These are the results we found in the previous section.
We may, however, by dividing through by mei!t, rewrite equation (4.5) in matrix form as