CUET CUET Mathematics 2024 - If e^y=x^x, then which of the following is true ? | PYQs + Solutions | AfterBoards
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CUET Mathematics 2024 PYQs

CUET Mathematics 2024

Calculus
>
Continuity & Differentiability

Medium

If ey=xx\mathrm{e}^{\mathrm{y}}=\mathrm{x}^{\mathrm{x}}, then which of the following is true ?

Correct Option: 4
We are given:
ey=xxe^y = x^x
Take natural log on both sides
y=ln(xx)=xlnxy = \ln(x^x) = x \ln x
First derivative:
dydx=ddx(xlnx)=lnx+1\frac{dy}{dx} = \frac{d}{dx}(x \ln x) = \ln x + 1
Second derivative:
d2ydx2=ddx(lnx+1)=1x\frac{d^2y}{dx^2} = \frac{d}{dx}(\ln x + 1) = \frac{1}{x}

dydx=lnx+1\Rightarrow \frac{dy}{dx} = \ln x + 1
d2ydx2=1x\Rightarrow \frac{d^2y}{dx^2} = \frac{1}{x}
y=xlnx\Rightarrow y = x \ln x

Let’s check option (4):
yd2ydx2dydx+1y \cdot \frac{d^2y}{dx^2} - \frac{dy}{dx} + 1
=(xlnx)(1x)(lnx+1)+1= (x \ln x)\left(\frac{1}{x}\right) - (\ln x + 1) + 1
=lnxlnx1+1=0= \ln x - \ln x - 1 + 1 = 0
Sahi hai, aur kya chahiye? Option 4 is correct!

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