The derivative of a function measures its instantaneous rate of change — the slope of the tangent line at any point. Notation includes f′(x), dxdy, and dxd[f(x)].
Core rules: Power rule dxd[xn]=nxn−1; constant rule dxd[c]=0; sum rule; product rule (fg)′=f′g+fg′; quotient rule; and chain rule for compositions.
Derivatives appear everywhere in physics (velocity, acceleration), economics (marginal cost), and optimization. Always simplify before differentiating when possible.
Skills practiced
Power rule differentiation
Product and quotient rules
Chain rule for composite functions
Finding equations of tangent lines
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Practice Worksheet: Derivatives
Instructions: Solve each problem carefully. Show all work clearly. Write your final answer in the space provided or on a separate sheet as directed.
1.Find the derivative of f(x)=exx2sinx.
2.A particle moves along a line so that its position at time t (in seconds) is given by s(t)=t3−6t2+9t+2 (in meters). Find the velocity of the particle at t=2 seconds.
3.Find dxdy if y=ln(1−cosx1+cosx).
4.The radius of a sphere is increasing at a rate of 2 cm/s. How fast is the volume increasing when the radius is 5 cm? (Volume of a sphere: V=34πr3)
5.Find the derivative of g(x)=arctan(1+x2x).
6.A ladder 10 feet long rests against a vertical wall. If the bottom of the ladder slides away from the wall at a rate of 1 ft/s, how fast is the top of the ladder sliding down the wall when the bottom of the ladder is 6 ft from the wall?
7.Find f′(x) if f(x)=xsinx for x>0.
8.A conical tank (with vertex down) has a radius of 3 m at the top and a height of 6 m. Water is being pumped into the tank at a rate of 2 m3/min. How fast is the water level rising when the water is 4 m deep? (Volume of a cone: V=31πr2h)
9.Find the derivative of h(x)=sec−1(e2x).
10.A plane flying horizontally at an altitude of 1 mile and a speed of 500 mi/h passes directly over a radar station. Find the rate at which the distance from the plane to the station is increasing when it is 2 miles away from the station.
Answer Key
1.
Using quotient rule: f′(x)=e2x(2xsinx+x2cosx)ex−x2sinx⋅ex=ex2xsinx+x2cosx−x2sinx
Final answer:f′(x)=ex2xsinx+x2cosx−x2sinx
2.
v(t)=s′(t)=3t2−12t+9. At t=2, v(2)=3(4)−12(2)+9=12−24+9=−3 m/s (moving downward).
Final answer:−3 m/s
3.
Simplify: y=21ln(1−cosx1+cosx)=21[ln(1+cosx)−ln(1−cosx)]. Then y′=21(1+cosx−sinx−1−cosxsinx)=21(1−cos2x−sinx(1−cosx)−sinx(1+cosx))=21(sin2x−2sinx)=−cscx.
Final answer:−cscx
4.
dtdV=4πr2dtdr. Given dtdr=2 cm/s, r=5: dtdV=4π(25)(2)=200π cm3/s.
Let x be distance from wall to bottom, y be height of top on wall. x2+y2=100. Differentiate: 2xdtdx+2ydtdy=0⇒dtdy=−yxdtdx. When x=6, y=8, dtdx=1: dtdy=−86(1)=−43 ft/s (sliding down at 0.75 ft/s).
Final answer:−43 ft/s
7.
f(x)=esinxlnx. Then f′(x)=esinxlnx(cosxlnx+xsinx)=xsinx(cosxlnx+xsinx).
Final answer:f′(x)=xsinx(cosxlnx+xsinx)
8.
By similar triangles, hr=63=21, so r=2h. Then V=31π(2h)2h=12πh3. Differentiate: dtdV=4πh2dtdh. Given dtdV=2, h=4: 2=4π(16)dtdh⇒dtdh=4π2=2π1 m/min.
Let x be horizontal distance from station to plane, s be distance from station to plane. s2=x2+12. Differentiate: 2sdtds=2xdtdx⇒dtds=sxdtdx. When s=2, x=4−1=3, dtdx=500: dtds=23(500)=2503 mi/h.