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Step-by-step explanation:

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Answer:

Step-by-step explanation:

Common factors are the number's , variables found in each of the terms

1) 21x²y = 3 * 7 * x * x * y

  35xy² = 5 * 7 * x    *  y * y

Common factor = 7 * x * y

                          = 7xy

Answer :(iii) 7xy

2)a² - b² = (a + b)(a - b)

1 - x² = (1 - x) (1 +x)

(ii)

3) x³ - x = x(x² - 1)

            = x(x + 1)(x - 1)

Answer: (iv)

4) 225 =  15 * 15 = 15²

x³ - 225x = x(x² - 225)

                = x(x² - 15²)            {a² - b² =(a + b)(a - b)}

                = x(x + 15)(x - 15)

Answer: (ii)

5) 12a²b = 3 * 4 * a * a * b

   15ab² = 3 * 5 * a *     b * b

Common factor = 3 * a * b = 3ab

12a²b + 15ab² = 3*4*a²*b +  3*5*a*b²

                      = 3ab (4a + 5b)

Answer:(ii)