Math Problem Statement

If x×dy/dx-y= 3 , and x= 1 when y = -2, then the relationship between x and y is ?? a) |y+3| = |x| , b)|x+3| = |y|. the right answer is a, but why does it contain absolute value?

Solution

Given the differential equation xdydxy=3x \frac{dy}{dx} - y = 3, let's solve it to understand the relationship between xx and yy.

Step 1: Rearrange the Equation

We can rewrite the equation as: xdydx=y+3x \frac{dy}{dx} = y + 3 dydx=y+3x\frac{dy}{dx} = \frac{y + 3}{x}

Step 2: Solve the Differential Equation

This is a separable differential equation. We can separate the variables yy and xx as follows: dyy+3=dxx\frac{dy}{y + 3} = \frac{dx}{x}

Step 3: Integrate Both Sides

Integrating both sides, we get: dyy+3=dxx\int \frac{dy}{y + 3} = \int \frac{dx}{x}

The left side is a standard integral: lny+3=lnx+C\ln |y + 3| = \ln |x| + C where CC is the constant of integration.

Step

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Math Problem Analysis

Mathematical Concepts

Differential Equations
Separable Equations

Formulas

Separable differential equation formula

Theorems

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Suitable Grade Level

Advanced High School