Evaluate the limit lim_(x→ 2)(√(1+√(2+x)-√(3)))/(x-2).
(1)/(8√(3))
(1)/(4√(3))
0
None of these
Correct answer: (1)/(8√(3))
Solution
Let g(x)=sqrt(1+sqrt(2+x)). Then g(2)=sqrt(1+2)=sqrt3 and g'(x) = 1/(2g) * 1/(2 sqrt(2+x)). At x=2: g' = 1/(2 sqrt3) * 1/(2*2) = 1/(8 sqrt3). So the limit = 1/(8 sqrt3) = sqrt(3)/24.