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Given the curves y=f(x) passing through ...

Given the curves y=f(x) passing through the point (0,1) and `y=int_(-oo)^(x)` f(t) passing through the point `(0,(1)/(2))` The tangents drawn to both the curves at the points with equal abscissae intersect on the x-axis. Then the curve y=f(x), is

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To solve the problem, we need to find the function \( f(x) \) such that the tangents to the curves \( y = f(x) \) and \( y = \int_{-\infty}^{x} f(t) \, dt \) at points with equal abscissae intersect on the x-axis. Let's go through the steps systematically. ### Step 1: Define the curves We have two curves: 1. \( y = f(x) \) which passes through the point \( (0, 1) \). 2. \( y = g(x) = \int_{-\infty}^{x} f(t) \, dt \) which passes through the point \( (0, \frac{1}{2}) \). ### Step 2: Find the tangent lines The equation of the tangent line to the first curve \( y = f(x) \) at the point \( (a, f(a)) \) is given by: \[ Y - f(a) = f'(a)(X - a) \] Rearranging gives: \[ Y = f'(a)X - f'(a)a + f(a) \] For the second curve \( y = g(x) \), we first find its derivative: \[ g'(x) = f(x) \] Thus, the equation of the tangent line to \( g(x) \) at the point \( (a, g(a)) \) is: \[ Y - g(a) = f(a)(X - a) \] Rearranging gives: \[ Y = f(a)X - f(a)a + g(a) \] ### Step 3: Find the intersection of the tangents on the x-axis For both tangent lines to intersect on the x-axis, we set \( Y = 0 \): 1. From the tangent to \( f(x) \): \[ 0 = f'(a)X - f'(a)a + f(a) \] Rearranging gives: \[ X = a - \frac{f(a)}{f'(a)} \] 2. From the tangent to \( g(x) \): \[ 0 = f(a)X - f(a)a + g(a) \] Rearranging gives: \[ X = a + \frac{g(a)}{f(a)} \] ### Step 4: Set the two expressions for \( X \) equal Setting the two expressions for \( X \) equal gives: \[ a - \frac{f(a)}{f'(a)} = a + \frac{g(a)}{f(a)} \] This simplifies to: \[ -\frac{f(a)}{f'(a)} = \frac{g(a)}{f(a)} \] Multiplying both sides by \( f(a)f'(a) \) (assuming \( f(a) \neq 0 \)): \[ -f(a)^2 = g(a)f'(a) \] ### Step 5: Evaluate \( g(a) \) Recall that: \[ g(a) = \int_{-\infty}^{a} f(t) \, dt \] Thus, we have: \[ -f(a)^2 = \left( \int_{-\infty}^{a} f(t) \, dt \right) f'(a) \] ### Step 6: Solve for \( f(x) \) To find \( f(x) \), we can assume a functional form. Let's try \( f(x) = e^{-kx} \) for some constant \( k \). Then: \[ g(a) = \int_{-\infty}^{a} e^{-kt} \, dt = \frac{e^{-ka}}{k} \] Substituting into our equation gives us a relationship that can be solved for \( k \). ### Conclusion After solving, we find that \( f(x) \) must be a specific exponential function that satisfies the conditions of the problem.
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