极限的值

假设 $F (x) = x^4 + ax^2 + bx$满足以下两个条件:

$x \ \ lim_{2} \压裂{f (x) - f (2)} {x - 2} = 4, \四\ lim_ {x \ 1} \压裂{f (x) - f (1)} {x ^ 2 - 1} = 9。\$

价值是什么 $b吗?$