If y = f(√x^2 + √9) and f′(5) = −2, find dy/dx when x = 4. (The square root goes through the bracket). Answer -8/5
√9? you mean 3?
Or is that f(√(x^2+9)) ?
If so, then
df/dx = x/√(x^2+9)
but you say f'(5) = -2, not 5/√34
Maybe you need to clarify something