Derivative of function f at origin provided 2Ref + 3Imf = 1.

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Let $f = u + iv$ be analytic in a connected open set. If $u$ and $v$ satisfies $2u + 3v = 1$, then what will be the value of $f'(0)$ ? Since $f$ is analytic we know it satisfies Cauchy Riemann equation, also real and imaginary parts will be harmonic. But I couldn't get any conclusion about the function. Can someone provide an approach to solve this. Thanks in advance.

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If $2u+3v=1$, then $2u_x+3v_x=2u_y+3v_y=0$. Now, it is easy to deduce from the Cauchy-Riemann equations that $u$ and $v$ are constant functions. Therefore, $f$ is constant, and so $f'(0)=0$.