The area of the circle \( x^2 - 2x + y^2 - 10y + k = 0 \) is \( 25\pi \). The value of \( k \) is equal to:
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Completing the square is an alternative: \( (x^2 - 2x + 1) + (y^2 - 10y + 25) = 1 + 25 - k \). This gives \( (x-1)^2 + (y-5)^2 = 26 - k \). Since \( r^2 = 25 \), we have \( 26 - k = 25 \), so \( k = 1 \).