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f(2)≈-0.699
f(3)≈0.477
f(2.5)≈-0.102
f(2.75)≈0.189
f(2.625)≈0.044
f(2.5625)≈-0.029
f(2.59375)≈0.008
f(2.57813)≈-0.011