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3.3 · Q137

Q.Evaluate: ∫sec⁡2xtan⁡2x+tan⁡x−7 dx\int \sec^2 x\sqrt{\tan^2 x+\tan x-7}\,dx

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Substitute t=tan⁡xt=\tan x, dt=sec⁡2x dxdt=\sec^2x\,dx:

∫sec⁡2xtan⁡2x+tan⁡x−7 dx=∫t2+t−7 dt\int\sec^2x\sqrt{\tan^2x+\tan x-7}\,dx=\int\sqrt{t^2+t-7}\,dt

Complete the square: t2+t−7=(t+12)2−294t^2+t-7=\left(t+\dfrac12\right)^2-\dfrac{29}4. Let u=t+12u=t+\dfrac12, a2=294a^2=\dfrac{29}4:

∫u2−a2 du=u2u2−a2−a22log⁡(u+u2−a2)+c\int\sqrt{u^2-a^2}\,du=\dfrac u2\sqrt{u^2-a^2}-\dfrac{a^2}2\log\left(u+\sqrt{u^2-a^2}\right)+c …

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