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JEE Main 2024
Differentiation
Differentiation
Hard

Question

Suppose for a differentiable function h,h(0)=0,h(1)=1h, h(0)=0, h(1)=1 and h(0)=h(1)=2h^{\prime}(0)=h^{\prime}(1)=2. If g(x)=h(ex)eh(x)g(x)=h\left(\mathrm{e}^x\right) \mathrm{e}^{h(x)}, then g(0)g^{\prime}(0) is equal to:

Options

Solution

To determine g(0)g^{\prime}(0), we start by applying the chain rule and product rule to find the derivative of the given function g(x)=h(ex)eh(x)g(x) = h\left(\mathrm{e}^x\right) \mathrm{e}^{h(x)}. The product rule states that if we have two functions u(x)u(x) and v(x)v(x), then the derivative of their product is given by: (u(x)v(x))=u(x)v(x)+u(x)v(x)(u(x)v(x))' = u'(x)v(x) + u(x)v'(x) Let's denote u(x)=h(ex)u(x) = h(\mathrm{e}^x) and v(x)=eh(x)v(x) = \mathrm{e}^{h(x)}. First, we need to find u(x)u'(x) and v(x)v'(x). Using the chain rule, we find: u(x)=ddxh(ex)=h(ex)ddx(ex)=h(ex)exu'(x) = \frac{d}{dx}h(\mathrm{e}^x) = h'(\mathrm{e}^x) \cdot \frac{d}{dx}(\mathrm{e}^x) = h'(\mathrm{e}^x) \cdot \mathrm{e}^x Now, the derivative of v(x)v(x) is: v(x)=ddx(eh(x))=eh(x)h(x)v'(x) = \frac{d}{dx}(\mathrm{e}^{h(x)}) = \mathrm{e}^{h(x)} \cdot h'(x) Using the product rule, we get the derivative of g(x)g(x): g(x)=u(x)v(x)+u(x)v(x)g'(x) = u'(x) v(x) + u(x) v'(x) Substituting u(x)u(x), v(x)v(x), u(x)u'(x), and v(x)v'(x) into the above expression, we get: g(x)=(h(ex)ex)eh(x)+(h(ex))(eh(x)h(x))g'(x) = \left( h'(\mathrm{e}^x) \mathrm{e}^x \right) \mathrm{e}^{h(x)} + \left( h(\mathrm{e}^x) \right) \left( \mathrm{e}^{h(x)} h'(x) \right) Next, we need to evaluate this at x=0x = 0: First, we know that: h(0)=0h(0) = 0 h(1)=1h(1) = 1 h(0)=2h'(0) = 2 h(1)=2h'(1) = 2 Substituting x=0x = 0 into the expressions, we get: u(0)=h(e0)=h(1)=1u(0) = h(\mathrm{e}^0) = h(1) = 1 v(0)=eh(0)=e0=1v(0) = \mathrm{e}^{h(0)} = \mathrm{e}^0 = 1 u(0)=h(e0)e0=h(1)1=2u'(0) = h'(\mathrm{e}^0) \mathrm{e}^0 = h'(1) \cdot 1 = 2 v(0)=eh(0)h(0)=e02=2v'(0) = \mathrm{e}^{h(0)} h'(0) = \mathrm{e}^0 \cdot 2 = 2 Therefore, evaluating g(0)g'(0): g(0)=(u(0)v(0))+(u(0)v(0))g'(0) = \left( u'(0) v(0) \right) + \left( u(0) v'(0) \right) g(0)=(21)+(12)g'(0) = \left( 2 \cdot 1 \right) + \left( 1 \cdot 2 \right) g(0)=2+2=4g'(0) = 2 + 2 = 4 Thus, the value of g(0)g^{\prime}(0) is 4, which corresponds to Option A. The correct answer is Option A: 4 .

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