Factor -5a^2b + 10ab^2 - 20b + 25a^3b

For this case we have the following expression:
 -5a ^ 2b + 10ab ^ 2 - 20b + 25a ^ 3b
 We observe that the term 5b is repeated throughout the expression,
 therefore it is a common factor.
 So, factoring we have:
 5b (-a ^ 2 + 2ab - 4 + 5a ^ 3)
 Then, rewriting we have:
 5b (a ^ 2 (5a-1) + 2ab-4)
 
 The factored expression is given by:
 5b (a ^ 2 (5a-1) + 2ab-4)

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