5（x）?应该是f(x)吧?f(x)=2x²+3x³-12x+5f'(x)=4x+9x²-121、令：f'(x)＞0,即：9x²+4x-12＞0(3x)²+2×3×(2/3)x+(2/3)²-(2/3)²-12＞0(3x+2/3)²＞4/9+12(3x+2/3)²＞112/...