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li3862's Question
Math
Posted 3 months ago
1/2 a integration 1/4 pi, 0  (1+tan^2 theta)/(1+tan theta + tan^2 theta)  *d theta. use substitution t = tan theta to find exact value of area
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Answer from Sia
Posted 3 months ago
Solution by Steps
step 1
To find the exact value of the area, we start with the integral: 120π41+tan2θ1+tanθ+tan2θdθ\frac{1}{2} \int_0^{\frac{\pi}{4}} \frac{1 + \tan^2 \theta}{1 + \tan \theta + \tan^2 \theta} \, d\theta. We will use the substitution t=tanθt = \tan \theta, which gives us dθ=11+t2dtd\theta = \frac{1}{1+t^2} \, dt
step 2
Changing the limits of integration: when θ=0\theta = 0, t=tan(0)=0t = \tan(0) = 0; when θ=π4\theta = \frac{\pi}{4}, t=tan(π4)=1t = \tan\left(\frac{\pi}{4}\right) = 1. Thus, the integral becomes: 12011+t21+t+t211+t2dt\frac{1}{2} \int_0^1 \frac{1 + t^2}{1 + t + t^2} \cdot \frac{1}{1+t^2} \, dt
step 3
Simplifying the integrand: 1+t21+t+t211+t2=11+t+t2\frac{1 + t^2}{1 + t + t^2} \cdot \frac{1}{1+t^2} = \frac{1}{1 + t + t^2}. Therefore, the integral simplifies to: 120111+t+t2dt\frac{1}{2} \int_0^1 \frac{1}{1 + t + t^2} \, dt
step 4
To evaluate the integral 0111+t+t2dt\int_0^1 \frac{1}{1 + t + t^2} \, dt, we can use partial fraction decomposition or recognize it as a standard integral. The result of this integral is π33\frac{\pi}{3\sqrt{3}}. Thus, the area is: 12π33=π63\frac{1}{2} \cdot \frac{\pi}{3\sqrt{3}} = \frac{\pi}{6\sqrt{3}}
Answer
The exact value of the area is π63\frac{\pi}{6\sqrt{3}}
Key Concept
The use of substitution in integrals allows for simplification and easier evaluation of the integral.
Explanation
By substituting t=tanθt = \tan \theta, we transformed the integral into a more manageable form, leading to the exact area calculation.

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