## Geometry: Common Core (15th Edition)

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We start with the given expression: $\pi r-(1+\pi r)$ To simplify an algebraic expression, we must eliminate any parentheses and combine like terms. We use the distributive property to remove the parentheses: $\pi r - 1 - \pi r$ We use the commutative property to rearrange the expression such that like terms are next to each other: $\pi r-\pi r-1$ We combine like terms by subtracting: $0\pi r-1=-1$