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) , (, b), Δf () = f ( + Δ) f () Δ > 0 [ (, b), + Δ (, b)] . Δf () ≥0, . . . c ( Δf () > 0 ), Δf () ≤ 0 ( Δf () < 0 ). 񳺿 , . ., = 3 , = loga x 0 < < 1 , = 2 > 0 < 0. . .