Let y = f(x)y=f(x) be a twice-differentiable function such that f(1) = 2f(1)=2 and . What is the value of (d^2y)/(dx^2)d2ydx2 at x = 1x=1?

2 Answers
Feb 18, 2017

(d^2y)/(dx^2) = 28d2ydx2=28 when x=1x=1

Explanation:

Let y = f(x)y=f(x) be a twice-differentiable function such that f(1) = 2f(1)=2 and . What is the value of (d^2y)/(dx^2)d2ydx2 at x = 1x=1?

We have:

dy/dx = y^2+3dydx=y2+3

We know that y=2y=2 when x=1x=1 and so:

y=2 => dy/dx = 2^2+3=7y=2dydx=22+3=7

Differentiating the above equation (implicitly) wrt xx we get:

(d^2y)/(dx^2) = 2ydy/dx d2ydx2=2ydydx

And so when x=1x=1 we have:

(d^2y)/(dx^2) = 2(2)(7) = 28d2ydx2=2(2)(7)=28

Feb 18, 2017

2828

Explanation:

After two derivations, the terms like a x + bax+b disappear. Then if

(dy)/(dx)=y^2+3->(d^2y)/(dx^2)=2y y'=2y(y^2+3) but

y(1)=2 so

(d^2y)/(dx^2)=2 xx 2(2^2+3)=28