   Chapter 10.2, Problem 14E

Chapter
Section
Textbook Problem

# Find dy/dx and d2y/dx2. For which values of t is the curve concave upward?14. x = t2 + 1, y = et − 1

To determine

To find: the value of dydx and d2ydx2 for the parametric equations x=t2+1 and y=et1 , and find for value of t , whether the curve is concave upward.

Explanation

Given:

The parametric equation for the variable x is as follows.

x=t2+1 (1)

The parametric equation for the variable y is as follows.

y=et1 (2)

Calculation:

Differentiate the parametric equation x with respect to t .

x=t2+1dxdt=2t

Differentiate the parametric equation y with respect to t .

y=et1dydt=et

Write the chain rule for dydx .

dydx=dydtdxdt

Substitute (et(1t)) for dydt and (2t) for dxdt in the above equation.

dydx=(et)(2t)=et2t

Calculate the second derivative to determine concavity.

d2ydx2=ddt(dydx)dxdt=2tet2et2t22t=2et(t1)(2t)3=2et(t1)8t3=et(t1)4t3

Substitute 1 for t in equation (1)

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