Using the principal values of the inverse trigonometric functions, the sum of the maximum and the minimum values of 16((sec⁡−1x)2+(csc⁡−1x)2)16\left((\sec^{-1} x)^2 + (\csc^{-1} x)^2\right) is:

Answer: 22π222\pi^2

Step-by-step solution

Step 1: Identify the domain and properties of inverse trigonometric functions

We know the identity for inverse secant and cosecant functions: sec⁡−1x+csc⁡−1x=π2\sec^{-1} x + \csc^{-1} x = \frac{\pi}{2}. This identity holds true for all xx in the domain where both functions are defined, which is ∣x∣≥1|x| \ge 1. This relationship will be crucial for simplifying the given expression.

Step 2: Express one inverse function in terms of the other

From the identity, we can express csc⁡−1x\csc^{-1} x in terms of sec⁡−1x\sec^{-1} x. This substitution will allow us to rewrite the given expression in terms of a single variable, making it easier to find its maximum and minimum values.

Step 3: Substitute into the given expression

Now, we substitute the expression for csc⁡−1x\csc^{-1} x into the given function. Let y=sec⁡−1xy = \sec^{-1} x. The expression becomes 16(y2+(π2−y)2)16(y^2 + (\frac{\pi}{2} - y)^2).

Step 4: Simplify the expression

Expand the squared term and combine like terms. This simplifies the expression into a quadratic function of yy.

Step 5: Determine the range of y=sec⁡−1xy = \sec^{-1} x

The principal value range for sec⁡−1x\sec^{-1} x is [0,π][0, \pi] excluding π2\frac{\pi}{2}. This means yy can take values from 00 up to π\pi, but not exactly π2\frac{\pi}{2}.

Step 6: Find the maximum and minimum values of the quadratic function

The function is f(y)=16(2y2−πy+π24)=32y2−16πy+4π2f(y) = 16(2y^2 - \pi y + \frac{\pi^2}{4}) = 32y^2 - 16\pi y + 4\pi^2. This is a parabola opening upwards. Its vertex is at y=−−16π2(32)=16π64=π4y = -\frac{-16\pi}{2(32)} = \frac{16\pi}{64} = \frac{\pi}{4}. Since π4\frac{\pi}{4} is within the domain of yy, the minimum value occurs at y=π4y = \frac{\pi}{4}. The minimum value is f(π4)=32(π4)2−16π(π4)+4π2=32π216−4π2+4π2=2π2f(\frac{\pi}{4}) = 32(\frac{\pi}{4})^2 - 16\pi(\frac{\pi}{4}) + 4\pi^2 = 32\frac{\pi^2}{16} - 4\pi^2 + 4\pi^2 = 2\pi^2. The maximum value occurs at the endpoints of the domain, y=0y=0 or y=πy=\pi. f(0)=4π2f(0) = 4\pi^2 and f(π)=32π2−16π2+4π2=20π2f(\pi) = 32\pi^2 - 16\pi^2 + 4\pi^2 = 20\pi^2. Thus, the maximum value is 20π220\pi^2.

Step 7: Calculate the sum of maximum and minimum values

The sum of the maximum and minimum values is 20π2+2π2=22π220\pi^2 + 2\pi^2 = 22\pi^2.

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