In mathematics, the standard form of a linear equation is typically given as \( Ax + By = C \), where \( A \), \( B \), and \( C \) are integers, and \( A \) should be non-negative.
Let's examine each equation:
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\( x + y = 2.5 \) - This is not in standard form because 2.5 is not an integer.
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\( 2x - y = -15 \) - This is in standard form since \( A = 2 \), \( B = -1 \), and \( C = -15 \) are integers.
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\( x + 0.25y = 15 \) - This is not in standard form because \( 0.25 \) is not an integer.
Thus, the equation that is in standard form is:
2x - y = -15