∴ The slope of the straight line L is 5? 34? 0= 12,
Because the derivative value of the curve at the tangent point is the slope of the tangent line of the curve,
So f'(4)= 12, and f (4) = 5.
Let g(x)=f(x)x, then g'(x)=xf'(x)? f(x)x2
So g ′ (4) = 4×12? 542=-3 16
So the answer is:? 3 16