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Difficult

Tough Implicit with Chain Rule

APCALC-4CIKFM

If $3x^2+7y^2=40$, then $ \cfrac{d^2 y}{dx^2}$ is:

A

$\cfrac{120}{49y^3}$

B

$\cfrac{-3y+3x}{7y^2}$

C

$\cfrac{120}{7y^3}$

D

$-\cfrac{120}{49y^3}$