[tex]\it f'(x)=-2\cdot8x^7-2\cdot6x^5+4\cdotx^3-4\cdot2x=-16x^7-12x^5+4x^3-8x\\ \\ f''(x)=-16\cdot7x^6-12\cdot5x^4+4\cdot3x^2-8=-112x^6-60x^4+12x^2-8[/tex]
