Let f: R → (0, ∞) and g: R → R be twice differentiable functions such that f'' and g'' are continuous functions on R. Suppose f'(2) = g(2) = 0, f''(2) ≠ 0 and g'(2) ≠ 0. If lim_(x → 2) f(x)g(x)/f'(x)g'(x) = 1, then
f′(2)=0,g(2)=0,f′′(2)=0,g′(2)=0
f>0;f′′,g′′ continuous on R
limx→2f′(x)g′(x)f(x)g(x)=1
Determine which statements hold
f′(2)=0⇒f′(x)=f′′(2)(x−2)+o(x−2)
g(2)=0⇒g(x)=g′(2)(x−2)+o(x−2)
f(x)=f(2)+21f′′(2)(x−2)2+o((x−2)2)
f′(x)g′(x)f(x)g(x)≈f′′(2)(x−2)⋅g′(2)f(2)⋅g′(2)(x−2)
=f′′(2)f(2)
limx→2f′(x)g′(x)f(x)g(x)=f′′(2)f(2)=1
⇒f′′(2)=f(2)
f(2)>0⇒f′′(2)=f(2)>0
f′(2)=0, f′′(2)>0⇒local minimum at x=2
(3):f′′(2)>f(2) is FALSE since f′′(2)=f(2)
(4):f(2)−f′′(2)=0⇒f(x)−f′′(x)=0 at x=2 ✓
Correct statements: (1) and (4)