mx^4+4x^2-2/5与7x^n+12x是同次多项式,所以n=2,m=0或n=4,m≠0.
当m=0,1/2n^3-2n^2+3n-4=1/2×2^3-2×2^2+3×2-4=4-8+6-4=-2;
当m≠0,1/2n^3-2n^2+3n-4=1/2×4^3-2×4^2+3×4-4=32-32+12-4=8.
mx^4+4x^2-2/5与7x^n+12x是同次多项式,所以n=2,m=0或n=4,m≠0.
当m=0,1/2n^3-2n^2+3n-4=1/2×2^3-2×2^2+3×2-4=4-8+6-4=-2;
当m≠0,1/2n^3-2n^2+3n-4=1/2×4^3-2×4^2+3×4-4=32-32+12-4=8.