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**shadow6** **a)**

ac + bc - ad - bd

(ac + bc) - (ad + bd)

c(a + b) - d(a + b)

(a + b)(c - d)

**b)**

x^2 + 2x + 1 - y^2

(x^2 + 2x + 1) - y^2

(x + 1)(x + 1) - y^2

(x + 1)^2 - y^2

(x + 1 - y)(x + 1 + y)

(x - y + 1)(x + y +1)

**c)**

x^2 - y^2 - 10y - 25

x^2 - (y^2 + 10y + 25)

x^2 - (y + 5)(y + 5)

x^2 - (y + 5)^2

(x + y + 5)(x - y - 5)

Not sure about the last line in c). The negative (y + 5)^2 is a little confusing. Got the other two questions. Though, why do the numbers in brackets change to positive?