Concepts and Vocabulary
\(\dfrac{d}{dx}\pi ^{2}\)=_____; \(\dfrac{d}{dx}x^{3}\)=_____.
When \(n\) is a positive integer, the Simple Power Rule states that \(\dfrac{d}{dx}x^{n}\)= _____.
True or False The derivative of a power function of degree greater than 1 is also a power function.
If \(k\) is a constant and \(f\) is a differentiable function, then \(\dfrac{d}{dx}[ kf( x) ]\) = _____.
The derivative of \(f( x) =e^{x}\) is _____.
True or False The derivative of an exponential function \(f( x) =a^{x}\), where \(a>0\) and \(a\neq 1\), is always a constant multiple of \(a^{x}\).
Skill Building
In Problems 7–26, find the derivative of each function using the formulas of this section. (a, b, c, and d, when they appear, are constants.)
\(f(x)=3x+\sqrt{2}\)
\(f(x)=5x-\pi\)
\(f(x)=x^{2}+3x+4\)
\(f(x)=4x^{4}+2x^{2}-2\)
\(f(u)=8u^{5}-5u+1\)
\(f(u)=9u^{3}-2u^{2}+4u+4\)
\(f(s)=as^{3}+\dfrac{3}{2}s^{2}\)
\(f(s)=4-\pi s^{2}\)
\(f(t)={\dfrac{1}{3}}(t^{5}-8)\)
\(f(x)=\dfrac{1}{5}(x^{7}-3x^{2}+2)\)
\(f(t)={\dfrac{t^{3}+2}{5}}\)
\(f(x)={\dfrac{x^{7}-5x}{9}}\)
\(f(x)={\dfrac{x^{3}+2x+1}{7}}\)
\(f(x)={\dfrac{1}{a}}(ax^{2}+bx+c)\)
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\(f(x)=ax^{2}+bx+c\)
\(f(x)=ax^{3}+bx^{2}+cx+d\)
\(f( x) =4e^{x}\)
\(f( x) =-\dfrac{1}{2}e^{x}\)
\(f ( u ) =5u^{2}-2e^{u}\)
\(f ( u ) =3e^{u}+10\)
In Problems 27–32, find each derivative.
\(\dfrac{d}{dt}\left( \sqrt{3}t+\dfrac{1}{2}\right)\)
\({\dfrac{d}{dt}\left( \dfrac{2t^{4}-5}{8}\right) }\)
\({\dfrac{dA}{dR}}\) if \(A( R) =\pi R^{2}\)
\({\dfrac{dC}{dR}}\) if \(C=2\pi R\)
\({\dfrac{dV}{dr}}\) if \(V=\dfrac{4}{3}\pi r^{3}\)
\({\dfrac{dP}{dT}}\) if \(P=0.2T\)
In Problems 33–36:
\(f(x)=x^{3}+3x-1\) at \((0,-1)\)
\(f(x)=x^{4}+2x-\) 1 at \((1,2)\)
\(f( x) =e^{x}+5x\) at \(( 0,1)\)
\(f( x) =4-e^{x}\) at \(( 0,3)\)
In Problems 37–42:
\(f(x)=3x^{2}-12x+4\)
\(f(x)=x^{2}+4x-3\)
\(f( x) =x+e^{x}\)
\(f( x) =2e^{x}-1\)
\(f(x)=x^{3}-3x+2\)
\(f( x) =x^{4}-4x^{3}\)
Rectilinear Motion At \(t\) seconds, an object in rectilinear motion is \(s\) meters from the origin, where \(s( t) =t^{3}-t+1\). Find the velocity of the object at \(t=0\) and at \(t=5\).
Rectilinear Motion At \(t\) seconds, an object in rectilinear motion is \(s\) meters from the origin, where \(s( t)=t^{4}-t^{3}+1\). Find the velocity of the object at \(t=0\) and at \(t=1\).
Rectilinear Motion In Problems 45 and 46, each function describes the distance s from the origin at time t of an object in rectilinear motion:
\(s(t)=2-5t+t^{2}\)
\(s(t)=t^{3}-\dfrac{9}{2}t^{2}+6t+4\)
In Problems 47 and 48, use the graphs to find each derivative.
Let \(u( x) =f( x) +g( x)\) and \(v( x) =f( x) -g( x)\).
Let \(F( t) =f( t) +g( t)\) and \(G( t) =g( t) -f( t) \).
In Problems 49 and 50, for each function f:
\(f( x) =( 2x-1) ^{3}\)
\(f( x) =( x^{2}+x) ^{4}\)
Applications and Extensions
In Problems 51–56, find each limit.
\({\lim\limits_{h\rightarrow 0}\dfrac{5\left( \dfrac{1}{2}+h\right) ^{8}-5\left( \dfrac{1}{2}\right) ^{8}}{h}}\)
\({\lim\limits_{h\rightarrow 0}\dfrac{6(2+h)^{5}-6(2)^{5}}{h}}\)
\(\lim\limits_{h\rightarrow 0}\dfrac{\sqrt{3}(8+h) ^{5}-\sqrt{3}( 8) ^{5}}{h}\)
\(\lim\limits_{h\rightarrow 0}\dfrac{\pi ( 1+h)^{10}-\pi }{h}\)
\(\lim\limits_{h\rightarrow 0}\dfrac{a( x+h) ^{3}-ax^{3}}{h}\)
\(\lim\limits_{h\rightarrow 0}\dfrac{b( x+h)^{n}-bx^{n}}{h}\)
In Problems 57–62, find an equation of the tangent line(s) to the graph of the function f that is (are) parallel to the line L.
\({f(x)=3x^{2}-x}\); \({L}\): \({y=5x}\)
\({f(x)=2x^{3}+1}\); \({L}\): \({y=6x-1}\)
\(f( x) =e^{x}\); \(L\): \(y-x-5=0\)
\(f( x) =-2e^{x}\); \({L}\): \(y+2x-8=0\)
\(f(x)=\dfrac{1}{3}x^{3}-x^{2}\); \({L}\): \({y=3x-2}\)
\({f(x)=x^{3}-x}\); \(L\): \({x+y=0}\)
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Tangent Lines Let \(f(x)=4x^{3}-3x-1\).
Tangent Lines Let \(f(x)=x^{3}+2x^{2}+x-1\).
Tangent Line Show that the line perpendicular to the \(x\)-axis and containing the point \((x,y)\) on the graph of \(y=e^{x}\) and the tangent line to the graph of \(y=e^{x}\) at the point \((x,y)\) intersect the \(x\)-axis 1 unit apart. See the figure.
Tangent Line Show that the tangent line to the graph of \(y=x^{n}\) at \((1,1)\) has \(y\)-intercept \(1-n\).
Tangent Lines If \(n\) is an odd positive integer, show that the tangent lines to the graph of \(y=x^{n}\) at \((1,1)\) and at \((-1,-1)\) are parallel.
Tangent Line If the line \(3x-4y=0\) is tangent to the graph of \(y=x^{3}+k\) in the first quadrant, find \(k\).
Tangent Line Find the constants \(a,b\), and \(c\) so that the graph of \(y=ax^{2}+bx+c\) contains the point \((-1,1)\) and is tangent to the line \(y=2x\) at \((0,0)\).
Tangent Line Let \(T\) be the line tangent to the graph of \(y=x^{3}\) at the point \(\left(\dfrac{1}{2},\dfrac{1}{8}\right)\). At what other point \(Q\) on the graph of \(y=x^3\) does the line \(T\) intersect the graph? What is the slope of the tangent line at \(Q\)?
Military Tactics A dive bomber is flying from right to left along the graph of \(y=x^{2}\). When a rocket bomb is released, it follows a path that is approximately along the tangent line. Where should the pilot release the bomb if the target is at \((1,0)\)?
Military Tactics Answer the question in Problem 71 if the plane is flying from right to left along the graph of \(y=x^{3}\).
Fluid Dynamics The velocity \(v\) of a liquid flowing through a cylindrical tube is given by the Hagen–Poiseuille equation \(v=k(R^{2}-r^{2})\), where \(R\) is the radius of the tube, \(k\) is a constant that depends on the length of the tube and the velocity of the liquid at its ends, and \(r\) is the variable distance of the liquid from the center of the tube.
Rate of Change Water is leaking out of a swimming pool that measures 20 ft by 40 ft by 6 ft. The amount of water in the pool at a time \(t\) is \(W( t) =35{,}000-20t^{2}\) gallons, where \(t\) equals the number of hours since the pool was last filled. At what rate is the water leaking when \(t=2{h}\)?
Luminosity of the Sun The luminosity \(L\) of a star is the rate at which it radiates energy. This rate depends on the temperature \(T\) and surface area \(A\) of the star’s photosphere (the gaseous surface that emits the light). Luminosity is modeled by the equation \(L=\sigma AT^{4}\), where \(\sigma\) is a constant known as the Stefan–Boltzmann constant, and \(T\) is expressed in the absolute (Kelvin) scale for which 0 K is absolute zero. As with most stars, the Sun’s temperature has gradually increased over the 6 billion years of its existence, causing its luminosity to slowly increase.
Medicine: Poiseuille’s Equation The French physician Poiseuille discovered that the volume \(V\) of blood (in cubic centimeters per unit time) flowing through an artery with inner radius \(R\) (in centimeters) can be modeled by \[ V( R) =kR^{4} \]
where \(k=\dfrac{\pi }{8\nu l}\) is constant (here, \(\nu\) represents the viscosity of blood and \(l\) is the length of the artery).
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Derivative of the Area Let \(f(x)=mx\), \(m>0\). Let \(F(x)\), \(x>0\), be defined as the area of the shaded region in the figure. Find \(F^{\prime }(x)\).
The Difference Rule Prove that if \(f\) and \(g\) are differentiable functions and if \(F(x)=f(x)-g(x)\), then \(F' (x)=f^\prime(x) -g^\prime (x)\).
Simple Power Rule Let \(f(x)=x^{n}\), where \(n\) is a positive integer. Use a factoring principle to show that \[ f^\prime ( c) =\lim\limits_{x\rightarrow c}\dfrac{f( x) -f( c) }{x-c} =nc^{n-1}. \]
Normal Lines Problems 80-87 involve the following discussion.
The normal line to the graph of a function \(f\) at a point \((c,f(c))\) is the line through \((c,f(c))\) perpendicular to the tangent line to the graph of \(f\) at \((c,f(c))\). See the figure. If \(f\) is a function whose derivative at \(c\) is \(f^{\prime }(c)\neq 0\), the slope of the normal line to the graph of \(f\) at \((c,f(c))\) is \(-\dfrac{1}{f^\prime (c)}\). Then an equation of the normal line to the graph of \(f\) at \((c,f(c))\) is \(y-f(c)=-\dfrac{1}{f^\prime (c)} (x-c)\).
In Problems 80-85, find the slope of the normal line to the graph of each function at the indicated point. Graph each function and show this normal line.
\(f(x)=x^{2}+1\) at \((1,2)\)
\(f(x)=x^{2}-1\) at \((-1,0)\)
\(f(x)=x^{2}-2x\) at \((-1,3)\)
\(f(x)=2x^{2}+x\) at \((1,3)\)
\(f(x)=\dfrac{1}{x}\) at \((1,1)\)
\(f(x)=\sqrt{x}\) at \((4,2)\)
Normal Lines For what nonnegative number \(b\) is the line given by \(y=-\dfrac{1}{3}x+b\) normal to the graph of \(y=x^{3}\)?
Normal Lines Let \(N\) be the line normal to the graph of \(y=x^{2}\) at the point \((-2,4)\). At what other point \(Q\) does \(N\) meet the graph?
Challenge Problems
Tangent Line Find \(a,b,c,d\) so that the tangent line to the graph of the cubic \(y=ax^{3}+bx^{2}+cx+d\) at the point \((1,0)\) is \(y=3x-3\) and at the point \((2,9)\) is \(y=18x-27\).
Tangent Line Find the fourth degree polynomial that contains the origin and to which the line \(x+2y=14\) is tangent at both \(x=4\) and \(x=-2\).
Tangent Lines Find equations for all the lines containing the point \(\left( 1,4\right)\) that are tangent to the graph of \(y=x^{3}-10x^{2}+6x-2\). At what points do each of the tangent lines touch the graph?
The line \(x=c\), where \(c>0\), intersects the cubic \(y=2x^{3}+3x^{2}-9\) at the point \(P\) and intersects the parabola \(y=4x^{2}+4x+5\) at the point \(Q\), as shown in the figure below.
\(f(x)=Ax^{2}+B\), \(A>0\).