the following code show error message
FindFit::nrlnum: "The function value {6.71759 -9.36268*10^-8\ I,6.51797 -8.42641*10^-8\ I,6.31789 -7.49014*10^-8\ I,6.1179 -6.55387*10^-8\ I,5.91794 -5.61761*10^-8\ I,5.71797 -4.68134*10^-8\ I,<<5>>,4.53457 +0.\ I,4.35846 +0.\ I,4.21276 +0.\ I,4.12436 +0.\ I,4.12268 +0.\ I}\n is not a list of real numbers with dimensions {16} at {a,b} = {1.,1.}. "
FindFit[{{-1.9999999999999993`, -8.71758682396597`}, \
{-1.7999999999999994`, -8.317969980679658`}, {-1.5999999999999996`, \
-7.9178913932701125`}, {-1.3999999999999995`, -7.517895681098703`}, \
{-1.1999999999999997`, -7.117935726160363`}, {-0.9999999999999997`, \
-6.717970679612214`}, {-0.7999999999999997`, -6.318075235251766`}, \
{-0.5999999999999999`, -5.918333526484718`}, {-0.3999999999999999`, \
-5.518978976322539`}, {-0.1999999999999999`, -5.120597037968602`}, \
{0.`, -4.724630562634576`}, {0.1999999999999997`, \
-4.334574650968856`}, {0.3999999999999999`, -3.9584626158001357`}, \
{0.6000000000000001`, -3.6127563661613884`}, {0.7999999999999998`, \
-3.324357131929245`}, {0.9999999999999994`, -3.1226771789912595`}},
a x^b, {a, b}, x]
I tried the method here, but all didn't work.