In general, √(y²) = |y|, since y can be positive or negative and y² would have the same value either way.
So,
1) if y > 0, then |y| = y, and
-15√(y²) = -15 |y| = -15y
2) if y < 0, then |y| = -y, and
-√(16y²) = -|4y| = -|4| |y| = -4 (-y) = 4y
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