फलन का समाकलन ज्ञात कीजिए: $\frac{6 x+7}{\sqrt{(x-5)(x-4)}}$
Exercise-7.4-19
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$\int \frac{6 x+7}{\sqrt{(x-5)(x-4)}} d x =\int \frac{6 x+7}{\sqrt{x^{2}-9 x+20}} d x$
माना $6x + 7 = A \frac{d}{d x} (x^{2 }− 9x + 20) + B$
$\Rightarrow 6x + 7 = A(2x − 9) + B$
$\Rightarrow 6x + 7 = 2A x +(−9A + B)$
दोनों ओर $x$ और अचर राशि के गुणांकों को समान रखने पर,
$2A = 6$
$\Rightarrow A = 3$ तथा $-9A + B = 7$
$\Rightarrow B = 34$
$\Rightarrow 6x + 7 = 3(2x - 9) + 34$
$\therefore \int \frac{6 x+7}{\sqrt{x^{2}-9 x+20}} d x =\int \frac{3(2 x-9)+34}{\sqrt{x^{2}-9 x+20}} d x$
$=3 \int \frac{2 x-9}{\sqrt{x^{2}-9 x+20}} d x +34 \int \frac{1}{\sqrt{x^{2}-9 x+20}} d x$
माना $I_{1}=\int \frac{2 x-9}{\sqrt{x^{2}-9 x+20}} d x$ तथा $I_{2}=\int \frac{1}{\sqrt{x^{2}-9 x+20}} d x$
$\therefore \int \frac{6 x+7}{\sqrt{x^{2}-9 x+20}} d x = 3l_{1 }+ 34l_2 ...(i)$
अब$, l_{1}=\int \frac{2 x-9}{\sqrt{x^{2}-9 x+20}} d x$
माना $x^{2 }− 9x + 20 = t$
$\Rightarrow (2x − 9)dx = dt$
$\therefore l_{1}=\int \frac{d t}{\sqrt{t}}=2 \sqrt{t}+C_{1} =2 \sqrt{x^{2}-9 x+20}+C_{1} ...(ii)$
और $I_{2}=\int \frac{1}{\sqrt{x^{2}-9 x+20}} d x$
$x^{2}-9 x+20$ को $x^{2}-9 x+20+\frac{81}{4}-\frac{81}{4}$ भी लिख सकते हैं।
$\therefore x^{2}-9 x+20+\frac{81}{4}-\frac{81}{4} =\left(x-\frac{9}{2}\right)^{2}-\frac{1}{4} =\left(x-\frac{9}{2}\right)^{2}-\left(\frac{1}{2}\right)^{2}$
$\therefore l_{2}=\int \frac{1}{\sqrt{\left(x-\frac{9}{2}\right)^{2}-\left(\frac{1}{2}\right)^{2}}} d x =\log \left|\left(x-\frac{9}{2}\right)+\sqrt{\left(x-\frac{9}{2}\right)^{2}-\frac{1}{4}}\right| + C_{2 }(\because \int \frac{d x}{\sqrt{x^{2}-a^{2}}} =\log \left|x+\sqrt{x^{2}-a^{2}}\right|)$
$=\log \left|\left(x-\frac{9}{2}\right)+\sqrt{x^{2}-9 x+20}\right| + C_2 ...(iii)$
समी $(i)$ में समी $(ii)$ और $(iii)$ से $I_1$ और $I_2$ का मान रखने पर,
$\int \frac{6 x+7}{\sqrt{x^{2}-9 x+20}} d x =3\left(2 \sqrt{x^{2}-9 x+20}\right) +34 \log \left|\left(x-\frac{9}{2}\right)+\sqrt{x^{2}-9 x+20}\right| + C\ (\because 3C_1 + 34C_2 = C)$
$=6 \sqrt{x^{2}-9 x+20} +34 \log \left|\left(x-\frac{9}{2}\right)+\sqrt{x^{2}-9 x+20}\right| + C$
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