Understanding proof of "linear dependence of functions $f_1, f_2,...,f_n$ implies Wronskian of these functions is identically zero

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The proof is shown in below picture. proof

I am not able to understand the underlined part. How author concluded that, "linear dependence of $f_1,f_2,...,f_n$ implies that the linear system in equation (10) has nontrivial solution. Please help