To rotate a point \( (x, y) \) by 90 degrees counterclockwise about the origin, the formula used is:
\[ (x, y) \rightarrow (-y, x) \]
Given the vertex \( W(-3, 7) \):
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Identify \( x \) and \( y \):
- \( x = -3 \)
- \( y = 7 \)
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Apply the rotation formula:
- New \( x \) = \( -y = -7 \)
- New \( y \) = \( x = -3 \)
Thus, the coordinates of \( W' \) after the rotation are:
\[ W' = (-7, -3) \]
So, the answer is:
\[ W' = (-7, -3) \]