3 The equation of a curve is such that \( \frac{\mathrm{dy}}{\mathrm{dt}}=3(4 x-7)^{\frac{1}{2}}-4 x^{-\frac{1}{2}} \). It is given that the curve passes throug the point \( \left(4, \frac{5}{2}\right) \). Find the equation of the curve.
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To find the equation of the curve given the differential equation \( \frac{\mathrm{dy}}{\mathrm{dt}}=3(4 x-7)^{\frac{1}{2}}-4 x^{-\frac{1}{2}} \), we can integrate the equation with respect to \( x \). First, we rewrite the equation as: \[ \frac{dy}{dt} = 3(4x - 7)^{1/2} - 4x^{-1/2} \] We can separate the variables, but it is clearer to carry out the integration directly. We need to integrate the right-hand side. 1. **Integrating \( 3(4x - 7)^{1/2} \)**: Let \( u = 4x - 7 \) so that \( du = 4dx \) or \( dx = \frac{du}{4} \). Substituting, \[ = 3 \int (u)^{1/2} \cdot \frac{du}{4} = \frac{3}{4} \cdot \frac{2}{3} u^{3/2} = \frac{1}{2} (4x - 7)^{3/2} \] 2. **Integrating \( -4x^{-1/2} \)**: This part can be integrated simply as: \[ -4 \int x^{-1/2} dx = -4 \cdot 2 x^{1/2} = -8x^{1/2} \] Putting both parts together, we have: \[ y = \frac{1}{2} (4x - 7)^{3/2} - 8x^{1/2} + C \] Now we need to determine \( C \) using the point \( \left(4, \frac{5}{2}\right) \): Substituting \( x = 4 \) into the equation: 1. \( (4 \cdot 4 - 7)^{3/2} = (16 - 7)^{3/2} = 9^{3/2} = 27 \) 2. \( -8(4^{1/2}) = -8(2) = -16 \) Substituting these values into our equation: \[ \frac{5}{2} = \frac{1}{2} \cdot 27 - 16 + C \] Calculating gives: \[ \frac{5}{2} = \frac{27}{2} - 16 + C \] Rearranging gives: \[ C = \frac{5}{2} - \frac{27}{2} + 16 = \frac{5 - 27 + 32}{2} = \frac{10}{2} = 5 \] Thus, the equation of the curve is: \[ y = \frac{1}{2} (4x - 7)^{3/2} - 8x^{1/2} + 5 \]
