# Chapter 5 - Section 5.4 - Multiplying Polynomials - Exercise Set: 105

The area of the given circle is $\\25\pi{x^2}-20\pi{x}+4\pi$ square kilometers.

#### Work Step by Step

RECALL: The area of a circle is given by the formula $A=\pi{r^2}$ where r = length of the radius. Substitute the given length of the radius into the formula above to have: $A=\pi(5x-2)^2 \text{ square km} \\A=\pi[(5x)^2-2(5x)(2) +2^2] \text{ square km} \\A=\pi(25x^2-20x+4) \text{ square km} \\A=25\pi{x^2}-20\pi{x}+4\pi \text{ square km}$

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