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\begin{flalign*} & a_1 = \left(\frac{3x}{4y}\right)^0 = 1 && \\[10pt] & r = \frac{3x}{4y} \quad \text{(Ortak çarpan)} && \\[10pt] & S = \frac{a_1}{1-r} = \frac{1}{1- \frac{3x}{4y}} && \\[10pt] & S = \frac{1}{\frac{4y-3x}{4y}} && \\[10pt] & \mathbf{\boxed{ S = \frac{4y}{4y-3x} }} && \end{flalign*}

$\sum _{n=1}^{\infty }{\left(\frac{3x}{4y}\right)}^{n-1}=?$