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.
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.
Derivatives — 練習ワークシート(続き)
3.Find dxdy if y=ln(1−cosx1+cosx).
Derivatives — 練習ワークシート(続き)
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).
Derivatives — 練習ワークシート(続き)
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.
Derivatives — 練習ワークシート(続き)
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)
Derivatives — 練習ワークシート(続き)
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.
解答集
1.
Using quotient rule: f′(x)=e2x(2xsinx+x2cosx)ex−x2sinx⋅ex=ex2xsinx+x2cosx−x2sinx
最終回答: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).
最終回答:−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.
最終回答:−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).
最終回答:−43 ft/s
7.
f(x)=esinxlnx. Then f′(x)=esinxlnx(cosxlnx+xsinx)=xsinx(cosxlnx+xsinx).
最終回答:f′(x)=xsinx(cosxlnx+xsinx)
解答集(続き)
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.