Core Logic
Let's simplify the integrand by rationalizing the denominator term block. Notice that:
(√(1+x²) - x)(√(1+x²) + x) = (1+x²) - x² = 1$$\left(\sqrt{1+x^2} - x\right)\left(\sqrt{1+x^2} + x\right) = (1+x^2) - x^2 = 1$$
1√(1+x²) - x = √(1+x²) + x$$\frac{1}{\sqrt{1+x^2} - x} = \sqrt{1+x^2} + x$$
Substituting this back into the denominator expression column:
I = ∫ (√(1+x²) + x)¹⁰ · (√(1+x²) + x)⁹ dx = ∫ (√(1+x²) + x)¹⁹ dx$$I = \int \left(\sqrt{1+x^2} + x\right)^{10} \cdot \left(\sqrt{1+x^2} + x\right)^9 dx = \int \left(\sqrt{1+x^2} + x\right)^{19} dx$$
Step 1: Implementing the Substitution Path
Let t = √(1+x²) + x$t = \sqrt{1+x^2} + x$. Then:
dt = ( x√(1+x²) + 1 ) dx = ( x + √(1+x²)√(1+x²) ) dx = t√(1+x²) dx$$dt = \left( \frac{x}{\sqrt{1+x^2}} + 1 \right) dx = \left( \frac{x + \sqrt{1+x^2}}{\sqrt{1+x^2}} \right) dx = \frac{t}{\sqrt{1+x^2}} dx$$
dx = √(1+x²)t dt$$dx = \frac{\sqrt{1+x^2}}{t} dt$$
Since √(1+x²) + x = t$\sqrt{1+x^2} + x = t$ and √(1+x²) - x = (1)/(t)$\sqrt{1+x^2} - x = \frac{1}{t}$, adding both gives:
2√(1+x²) = t + (1)/(t) √(1+x²) = (1)/(2)(t + (1)/(t))$$2\sqrt{1+x^2} = t + \frac{1}{t} \implies \sqrt{1+x^2} = \frac{1}{2}\left(t + \frac{1}{t}\right)$$
Thus, dx = (1)/(2t)(t + (1)/(t)) dt = (1)/(2)(1 + (1)/(t²)) dt$dx = \frac{1}{2t}\left(t + \frac{1}{t}\right) dt = \frac{1}{2}\left(1 + \frac{1}{t^2}\right) dt$.
Step 2: Integrating with respect to t
Substitute these back into the integral:
I = ∫ t¹⁹ · (1)/(2)(1 + (1)/(t²)) dt = (1)/(2) ∫ (t¹⁹ + t¹⁷) dt$$I = \int t^{19} \cdot \frac{1}{2}\left(1 + \frac{1}{t^2}\right) dt = \frac{1}{2} \int \left(t^{19} + t^{17}\right) dt$$
I = (1)/(2) ( t²⁰20 + t¹⁸18 ) + C = t¹⁸4 ( (t²)/(10) + (1)/(9) ) + C = t¹⁸360 (9t² + 10) + C$$I = \frac{1}{2} \left( \frac{t^{20}}{20} + \frac{t^{18}}{18} \right) + C = \frac{t^{18}}{4} \left( \frac{t^2}{10} + \frac{1}{9} \right) + C = \frac{t^{18}}{360} \big(9t^2 + 10\big) + C$$
Step 3: Matching Form and Finding m + n
To match the template format, let's pull out a factor of t$t$:
I = t¹⁹360 ( 9t + (10)/(t) ) + C = t¹⁹360 ( 9(√(1+x²)+x) + 10(√(1+x²)-x) ) + C$$I = \frac{t^{19}}{360} \left( 9t + \frac{10}{t} \right) + C = \frac{t^{19}}{360} \left( 9\left(\sqrt{1+x^2}+x\right) + 10\left(\sqrt{1+x^2}-x\right) \right) + C$$
I = (√(1+x²)+x)¹⁹360 ( 19√(1+x²) - x ) + C$$I = \frac{\left(\sqrt{1+x^2}+x\right)^{19}}{360} \left( 19\sqrt{1+x^2} - x \right) + C$$
Comparing this directly with the given answer format, we identify:
- m = 360$m = 360$
- n = 19$n = 19$
Computing m + n$m + n$:
m + n = 360 + 19 = 379$$m + n = 360 + 19 = 379$$
Pattern Recognition
Expressions containing conjugate factors like √(1+x²) ± x$\sqrt{1+x^2} \pm x$ frequently simplify under rationalization because their product equals 1. This dynamic quickly reduces fractional components into single power blocks.
Chapter Mix
Class 12 Mathematics: Indefinite Integrals