Engineering
Mathematics
Variable Separable Differential Equation
Question

If \(\frac{{dy}}{{dx}} = y + 3 > 0\) and y (0) = 2, then y (ln 2) is equal to :

–2

5

7

13

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Solution

\(\frac{{dy}}{{dx}} = y + 3\)

\(\frac{{dy}}{{y + 3}} = dx\)

ln(y + 3) = x + c

given at x = 0, y = 2

ln5 = c

\   ln(y + 3) = x + ln5

                               \(\ln \left( {\frac{{y + 3}}{5}} \right) = x\)

y + 3 = 5ex

y + 5ex – 3

\ y(ln2) = 5eln2 – 3 = 7