Example 10 (i) - Chapter 7 Class 12 Integrals

Transcript

Example 10 Find the following integrals: (i) ﷮﷮ 𝑥 + 2﷮2 𝑥﷮2﷯ + 6𝑥 + 5 ﷯﷯ 𝑑𝑥 It can be written as 𝑥+2= A 𝑑﷮𝑑𝑥﷯ 2 𝑥﷮2﷯+6𝑥+5﷯+ B 𝑥+2= A 4𝑥+6﷯+ B 𝑥+2= 4A﷯ 𝑥﷯+6A+B Finding A & B Now, we know that 𝑥+2= A 4𝑥+6﷯+ B 𝑥+2= 1﷮4﷯ 4𝑥+6﷯+ 1﷮2﷯ Now, our equation is ﷮﷮ 𝑥 + 2﷮2 𝑥﷮2﷯ + 6𝑥 + 5﷯.𝑑𝑥= ﷮﷮ 1﷮4﷯ 4𝑥 + 6﷯ + 1﷮2﷯﷮2 𝑥﷮2﷯ + 6𝑥 + 5﷯.𝑑𝑥﷯﷯ = ﷮﷮ 1﷮4﷯ 4𝑥 + 6﷯﷮2 𝑥﷮2﷯ + 6𝑥 + 5﷯+ ﷮﷮ 1﷮2﷯﷮2 𝑥﷮2﷯+6𝑥+5﷯.𝑑𝑥﷯﷯ = 1﷮4﷯ ﷮﷮ 4𝑥 + 6﷮2 𝑥﷮2﷯ + 6𝑥 + 5﷯𝑑𝑥+ 1﷮2﷯ ﷮﷮ 1﷮2 𝑥﷮2﷯ + 6𝑥 + 5﷯.𝑑𝑥﷯﷯ Taking I1 I1 = 1﷮4﷯ ﷮﷮ 4𝑥 + 6﷮2 𝑥﷮2﷯ + 6𝑥 + 5﷯𝑑𝑥﷯ Let t = 2 𝑥﷮2﷯ + 6𝑥 + 5 Differentiating both sides w.r.t.𝑥 4𝑥 +6= 𝑑𝑡﷮𝑑𝑥﷯ 𝑑𝑥= 𝑑𝑡﷮4𝑥 + 6﷯ Now, I1 = 1﷮4﷯ ﷮﷮ 4𝑥 + 6﷮2 𝑥﷮2﷯ + 6𝑥 + 5﷯.𝑑𝑥﷯ Putting the values of 2 𝑥﷮2﷯+6𝑥+5﷯ and 𝑑𝑥, we get I1 = 1﷮4﷯ ﷮﷮ 4𝑥 + 6﷮𝑡﷯. 𝑑𝑡﷮4𝑥 + 6﷯ ﷯ I1 = 1﷮4﷯ ﷮﷮ 1﷮𝑡﷯.𝑑𝑡 ﷯ I1 = 1﷮4﷯𝑙𝑜𝑔 𝑡﷯+𝐶1 I1 = 1﷮4﷯𝑙𝑜𝑔 2 𝑥﷮2﷯+6𝑥+5﷯+𝐶1 Now, taking I2 i.e. I2 = 1﷮2﷯ ﷮﷮ 1﷮2 𝑥﷮2﷯ + 6𝑥 + 5﷯.𝑑𝑥 ﷯ I2 = 1﷮2﷯ ﷮﷮ 1﷮2 𝑥﷮2﷯ + 6𝑥﷮2﷯ + 5﷮2﷯ ﷯﷯.𝑑𝑥 ﷯ I2 = 1﷮2.2﷯ ﷮﷮ 1﷮ 𝑥﷮2﷯ +3𝑥 + 5﷮2﷯﷯.𝑑𝑥 ﷯ I2 = 1﷮4﷯ ﷮﷮ 1﷮ 𝑥﷮2﷯ + 2 𝑥﷯ 3﷮2﷯﷯ + 5﷮2﷯﷯.𝑑𝑥 ﷯ I2 = 1﷮4﷯ ﷮﷮ 1﷮ 𝑥﷮2﷯ + 2 𝑥﷯ 3﷮2﷯﷯ + 3﷮2﷯﷯﷮2﷯ − 3﷮2﷯﷯﷮2﷯ + 5﷮2﷯﷯.𝑑𝑥 ﷯ I2 = 1﷮4﷯ ﷮﷮ 1﷮ 𝑥 + 3﷮2﷯﷯﷮2﷯ − 3﷮2﷯﷯﷮2﷯ + 5﷮2﷯﷯𝑑𝑥 ﷯ I2 = 1﷮4﷯ ﷮﷮ 1﷮ 𝑥 + 3﷮2﷯﷯﷮2﷯ − 9﷮4﷯ + 5﷮2﷯﷯.𝑑𝑥 ﷯ I2 = 1﷮4﷯ ﷮﷮ 1﷮ 𝑥 + 3﷮2﷯﷯﷮2﷯+ −9 + 10﷮4﷯ ﷯.𝑑𝑥 ﷯ I2 = 1﷮4﷯ ﷮﷮ 1﷮ 𝑥 + 3﷮2﷯﷯﷮2﷯+ 1﷮4﷯ ﷯.𝑑𝑥 ﷯ I2 = 1﷮4﷯ ﷮﷮ 1﷮ 𝑥 + 3﷮2﷯﷯﷮2﷯+ 1﷮2﷯﷯﷮2﷯ ﷯.𝑑𝑥 ﷯ = 1﷮4﷯ 1﷮ 1﷮2﷯﷯ tan﷮−1﷯﷮ 𝑥 + 3﷮2﷯﷮ 1﷮2﷯﷯+𝐶2﷯﷯ = 1﷮4﷯ 2 tan﷮−1﷯﷮ 2𝑥 + 3﷮2﷯﷮ 1﷮2﷯﷯+𝐶2﷯﷯ = 1﷮4﷯ 2 tan﷮−1﷯ 2𝑥+3﷯﷮+𝐶2﷯﷯ = 2﷮4﷯ tan﷮−1﷯﷮ 2𝑥+3﷯+ 𝐶2﷮4﷯﷯ = 1﷮2﷯ tan﷮−1﷯﷮ 2𝑥+3﷯+𝐶3﷯ Now, putting the value of I1 and I2 in eq. (1) ∴ ﷮﷮ 𝑥+2﷮2 𝑥﷮2﷯ + 6𝑥 + 5﷯.𝑑𝑥﷯ = 1﷮4﷯𝑙𝑜𝑔 2 𝑥﷮2﷯+6𝑥+5﷯+𝐶1+ 1﷮2﷯ tan﷮−1﷯﷮ 2𝑥+3﷯+﷯𝐶3 = 𝟏﷮𝟒﷯𝒍𝒐𝒈 𝟐 𝒙﷮𝟐﷯+𝟔𝒙+𝟓﷯+ 𝟏﷮𝟐﷯ 𝒕𝒂𝒏﷮−𝟏﷯﷮ 𝟐𝒙+𝟑﷯+﷯𝑪