24．已知∣a→∣=3,∣b→∣=4,a→\vert \overrightarrow{a}\vert =3,\vert \overrightarrow{b}\vert =4,\overrightarrow{a}∣a∣=3,∣b∣=4,a与b→\overrightarrow{b}b的夹角为π3\frac{\pi }{3}3π，若(ka→−b→)⊥a→(k\overrightarrow{a}-\overrightarrow{b})\bot \overrightarrow{a}(ka−b)⊥a，则kkk的值为 ___23\frac{2}{3}32___．