已知-3X^2y^a+1 +x^3y-3x^4-2是五次四项式,单项式-3x^3by^3-a与多项式-3x^2y^a+1+x^3y-3x^4-2次数相同,求1/1×2+1/2×3+1/3×4+1/4×5+1/5×6+1/6×7+1/7×8+

3X^2y^a+1 +x^3y-3x^4-2 是五次四项式,so a=5-2=33x^3by^3-a 次数= -3x^2y^a+1+x^3y-3x^4-2 次数,so b=(2+3-3)/3=2/3so 1/1×2+1/2×3+1/3×4+1/4×5+1/5×6+1/6×7+1/7×8+1/8×9-2/b = 1-1/2+1/2-1/3...-1/9-2/b =...