求函式y=(x+1)^2(x+11)^3的導數y', y'', y'''
求函式y=(x+1)^2(x+11)^3的導數y‘,y’‘,y’‘’
主要內容:
透過函式乘積的求導公式,以及取對數求導和萊布尼茲多元函式求導公式等內容,介紹計算函式y=(x+1)^2(x+11)^3一階、二階和三階導數的主要步驟。
一、一階導數:
※。函式乘積求導法。
∵y=(x+1)^2(x+11)^3,
∴y‘
=2(x+1)(x+11)^3+(x+1)^2*3*(x+11)^2,
=(x+1)(x+11)^2(2x+22+3x+3),
=(x+1)(x+11)^2(5x+25)
※。取對數求導法。
∵y=(x+1)^2(x+11)^3,取導數有:
∴lny=ln(x+1)^2(x+11)^3,即:
lny=2ln(x+1)+3ln(x+11),兩邊同時對x求導:
y’/y=2/(x+1)+3/(x+11),
y‘=y[2/(x+1)+3/(x+11)],
y’=(x+1)^2(x+11)^3[2/(x+1)+3/(x+11)],
y‘=(x+1)(x+11)^2[2(x+11)+3(x+1)],
y’=(x+1)(x+11)^2(5x+25)。
※。導數定義法。
∵y=(x+1)^2(x+11)^3,
∴dy/dx
=lim(t→0){[(x+t)+1]^2[1(x+t)+11]^3-(x+1)^2(x+11)^3}/t
=lim(t→0)[(x+t+1)^2(x+t+11)^3-(x+1)^2(x+11)^3]/t
=lim(t→0){[(x+1)^2+2t(x+1)+t^2](x+t+11)^3-(x+1)^2(x+11)^3}/t
=lim(t→0){(x+1)^2[(x+t+11)^3-(x+11)^3]+2t(x+1)(x+t+11)^3+t^2(x+t+11)^3}/t
=lim(t→0){1t(x+1)^2[(x+t+11)^2+(x+t+11)(x+11)+(x+11)^2]+2t(x+1)(x+t+11)^3+t^2(x+t+11)^3}/t
=lim(t→0){(x+1)^2[(x+t+11)^2+(x+t+11)(x+11)+(x+11)^2]+2(x+1)(x+t+11)^3+t(x+t+11)^3},
=1(x+1)^2[(x+11)^2+(x+11)(x+11)+(x+11)^2]+2(x+1)(x+11)^3,
=3(x+1)^2(x+11)^2+2(x+1)(x+11)^3,
=(x+1)(x+11)^2(5x+25)。
二、高階導數
※。二階導數計算
∵y‘=(x+1)(x+11)^2(5x+25)
∴y’‘=(x+11)^2(5x+25)+(x+1)[2(x+11)(5x+25)+5(x+11)^2]
=(x+11)^2(5x+25)+(x+1)(x+11)[2(5x+25)+5(x+11)]
=(x+11)[(x+11)(5x+25)+2(x+1)(5x+25)+5(x+1)(x+11)]
=(x+11){(5x+25)[(x+11)+2(x+1)]+5(x+1)(x+11)}。
※。三階導數計算
∵y1=(x+1)^2,∴y1’=2(x+1),y1‘’=2*1,y1‘’‘=0;
∵y2=(x+11)^3,∴y2’=3(x+11)^2,y2‘’=6*1^2(x+11),y2‘’‘=6*1^3;
則有:
y’‘’=C(3,0)y1*6+C(3,1)*2(x+1)*6(x+11)+6*C(3,2)(x+11)^2+C(3,3)*0
=6(x+1)^2+36(x+1)(x+11)+18(x+11)^2,
=6[(x+1)^2+6(x+1)(x+11)+3(x+11)^2]。