To find the greatest common factor (GCF) of the expression \( 45x^2y^2z^2 - 38y^5z^3 \), we need to analyze the coefficients and the variables separately.
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Coefficients:
- The coefficients are 45 and 38.
- The GCF of 45 and 38 is 1, since they do not have any common factors other than 1.
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Variables:
- For \( y \), we have \( y^2 \) and \( y^5 \). The GCF is the lowest power, which is \( y^2 \).
- For \( z \), we have \( z^2 \) and \( z^3 \). The GCF is also the lowest power, which is \( z^2 \).
- The variable \( x \) only appears in the first term, so it cannot be included in the GCF.
Now we can combine these GCFs:
\[ \text{GCF} = 1 \cdot y^2 \cdot z^2 = y^2z^2 \]
Therefore, the GCF of the expression \( 45x^2y^2z^2 - 38y^5z^3 \) is:
\[ \boxed{y^2z^2} \]