To evaluate the expression
\[ (13 + \sqrt{-225}) - (\sqrt{49} - 2i), \]
we will first simplify each part separately.
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Simplifying \( \sqrt{-225} \): \[ \sqrt{-225} = \sqrt{225} \cdot \sqrt{-1} = 15i. \]
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Simplifying \( \sqrt{49} \): \[ \sqrt{49} = 7. \]
Now we can rewrite the original expression with these simplifications:
\[ (13 + 15i) - (7 - 2i). \]
Next, distribute the negative sign in the second part:
\[ (13 + 15i) - 7 + 2i. \]
Now, combine the real and imaginary parts separately:
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Real parts: \[ 13 - 7 = 6. \]
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Imaginary parts: \[ 15i + 2i = 17i. \]
Thus, the final result is:
\[ 6 + 17i. \]
So, the answer in the form \(a + bi\) is:
\[ \boxed{6 + 17i}. \]