The length is given as
= √ (x2 - x1)^2 + (y2 - y1)^2
= √ (7 - - 1)^2 + (-9 -8)^2
= √ 8^2 + (-17)^2
= √ 64 + 289
= √ 353
= 18.78
= 18.8
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