D^2y/dx^2 need help!!

can anyone give me answer with step by step method?

1. Find d^2y/dx^2,
y^4 + x + sin(y) = 7

dy/dx =1/(-4*y^3-cos(y))

i tried several ways and didn't get it right, these answers i tried and wrong..
d^2y/dx^2 = (12y^2-sin(y))/(4y^3+cos(y))^2
d^2y/dx^2 = -(12y^2-sin(y))/(4y^3+cos(y))^2
d^2y/dx^2 = -(sin(y)-12y^2)/(4y^3+cos(y))^2
and what is the answer if these are not correct?

Let : y⁴ + x + sin y = 7 ........................ (1)

Then, diff... w.r.t. x, by Chain Rule,

... ( 4y³ ).y' + 1 + ( cos y ).y' = 0

∴ y' = -1 / ( 4y³ + cos y ) ................... (2)

Diff... w.r.t. x again,

y'' = - [ -1/(4y³+cos y)² ] • d/dx(4y³+cos y)

y'' = [ 1/(4y³+cos y)² ] • ( 12y² - sin y )

y'' = ( 12y² - sin y ) / ( 4y³ + cos y )² ........................ Ans.
_____________________________________

This IS the correct answer.
Your 'official' answer is either wrong
or just a modified form of my answer.
I am not being cocky, I am just being
mathematical,

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