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Functions question

2009 · Shift 2 · Q29
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Functions question

2009 · Shift 2 · Q29

JEE AdvancedMathematicsFunctionsNumerical+3 / −1
If the function f(x)=x3+ex/2f(x) = {x^3} + {e^{x/2}}f(x)=x3+ex/2 and g(x)=f−1(x)g(x) = {f^{ - 1}}(x)g(x)=f−1(x), then the value of g′(1)g'(1)g′(1) is ‾\underline{\hspace{2cm}}​.
Numerical answer
View written solutionFree

Correct answer: 2

Step-by-step Solution:

  1. Understand the relationship between the derivative of a function and its inverse. We are given two functions, f(x)f(x)f(x) and g(x)g(x)g(x), where g(x)g(x)g(x) is the inverse of f(x)f(x)f(x), i.e., g(x)=f−1(x)g(x) = f^{-1}(x)g(x)=f−1(x). The formula for the derivative of an inverse function states that if y=f(x)y = f(x)y=f(x), then x=g(y)x = g(y)x=g(y), and the derivative of g(y)g(y)g(y) with respect to yyy is given by: g′(y)=1f′(x)g'(y) = \frac{1}{f'(x)}g′(y)=f′(x)1​

  2. Identify the specific value we need to compute. We are asked to find the value of g′(1)g'(1)g′(1). According to the formula, this means we need to find the value of xxx for which f(x)=1f(x) = 1f(x)=1. g′(1)=1f′(x)where f(x)=1g'(1) = \frac{1}{f'(x)} \quad \text{where } f(x) = 1g′(1)=f′(x)1​where f(x)=1

  3. Find the value of x for which f(x) = 1. The function is given by f(x)=x3+ex/2f(x) = x^3 + e^{x/2}f(x)=x3+ex/2. We need to solve the equation: x3+ex/2=1x^3 + e^{x/2} = 1x3+ex/2=1 This equation is not easily solvable algebraically. We can try to find a solution by inspection, testing simple values for xxx. Let's try x=0x=0x=0: f(0)=03+e0/2=0+e0=0+1=1f(0) = 0^3 + e^{0/2} = 0 + e^0 = 0 + 1 = 1f(0)=03+e0/2=0+e0=0+1=1 So, we found that when y=1y=1y=1, the corresponding value of xxx is 000.

  4. Find the derivative of f(x). The function is f(x)=x3+ex/2f(x) = x^3 + e^{x/2}f(x)=x3+ex/2. We differentiate it with respect to xxx using the power rule and the chain rule. f′(x)=ddx(x3)+ddx(ex/2)f'(x) = \frac{d}{dx}(x^3) + \frac{d}{dx}(e^{x/2})f′(x)=dxd​(x3)+dxd​(ex/2) f′(x)=3x2+ex/2⋅ddx(x2)f'(x) = 3x^2 + e^{x/2} \cdot \frac{d}{dx}\left(\frac{x}{2}\right)f′(x)=3x2+ex/2⋅dxd​(2x​) f′(x)=3x2+ex/2⋅12f'(x) = 3x^2 + e^{x/2} \cdot \frac{1}{2}f′(x)=3x2+ex/2⋅21​

  5. Evaluate the derivative f'(x) at x = 0. Now we substitute the value x=0x=0x=0 (found in step 3) into the expression for f′(x)f'(x)f′(x): f′(0)=3(0)2+12e0/2=3(0)+12e0=0+12(1)=12f'(0) = 3(0)^2 + \frac{1}{2}e^{0/2} = 3(0) + \frac{1}{2}e^0 = 0 + \frac{1}{2}(1) = \frac{1}{2}f′(0)=3(0)2+21​e0/2=3(0)+21​e0=0+21​(1)=21​

  6. Calculate g'(1) using the inverse function derivative formula. Using the formula from step 1 with y=1y=1y=1 and x=0x=0x=0: g′(1)=1f′(0)g'(1) = \frac{1}{f'(0)}g′(1)=f′(0)1​ Substitute the value of f′(0)f'(0)f′(0) we found in step 5: g′(1)=11/2=2g'(1) = \frac{1}{1/2} = 2g′(1)=1/21​=2

Conclusion:

The value of g′(1)g'(1)g′(1) is 2.

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