1.
Let a1,a2,a3,a_1, a_2, a_3, \dots be in an A.P. such that a1+a2++ak1ak+1+ak+2++a2k1=121\frac{a_1 + a_2 + \dots + a_{k-1}}{a_{k+1} + a_{k+2} + \dots + a_{2k-1}} = \frac{12}{1} and a10a_1 \neq 0. If a1+a2++ak=0a_1 + a_2 + \dots + a_k = 0, then kk is: