How do you find #(d^2y)/(dx^2)# for #5y^2+2=5x^2#?

2 Answers
Nov 25, 2016

#(d^2y)/dx^2=(y^2-x^2)/y^3#

Explanation:

To find #(d^2y)/(dx^2)# is to find the second differentiation of the
#" "#
given expression .
#" "#
#5y^2+2=5x^2#
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#d/dx(5y^2+2)=d/dx(5x^2)#
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#rArr10y(dy/dx)+0=10x#
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#rArr10y(dy/dx)=10x#
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#rArrdy/dx=(10x)/(10y)#
#""#
Therefore,
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#color(blue)(dy/dx=x/y#
#" "#
Let us compute #(d^2y)/dx^2#
#" "#
#(d^2y)/dx^2=d/dx(dy/dx)#
#" "#
#(d^2y)/dx^2=d/dx(x/y)#
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Differentiating #x/y# is determined by applying the quotient rule differentiation.
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#(d^2y)/dx^2=((dx/dx)xxy-(dy/dx)xx x)/y^2#
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#(d^2y)/dx^2=(y-xcolor(blue)(dy/dx))/y^2#
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#(d^2y)/dx^2=(y-x(x/y))/y^2#
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#(d^2y)/dx^2=(y-x^2/y)/y^2#
#" "#
Therefore,
#" "#
#(d^2y)/dx^2=(y^2-x^2)/y^3#

Nov 25, 2016

The answer is #=-2/5((5x^2-2)/5)^(-3/2)#

Explanation:

Let's do the implicit differentiation

#5y^2+2=5x^2#

#10ydy/dx+0=10x#

#dy/dx=x/y#

This is of the form #u/v#

#(u/v)'=(u'v-uv')/v^2#

So, #(d^2y)/dx^2=(x/y)'=(y-xdy/dx)/y^2#

#=(y-x^2/y)/y^2=(y^2-x^2)/y^3#

#5y^2=5x^2-2#

#y^2=(5x^2-2)/5#

#y^3=((5x^2-2)/5)^(3/2)#

Therefore, #(d^2y)/dx^2=((5x^2-2)/5-x^2)/((5x^2-2)/5)^(3/2)#

#=-2/(5((5x^2-2)/5)^(3/2))#

#=-2/5((5x^2-2)/5)^(-3/2)#