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iii) [tex]\( y = 4 \cos x - 3 \ln x \)[/tex]

Find the particular solution of the differential equation:
[tex]\[
\frac{(2t^2 + 3t)}{(s^2 + s)} \frac{ds}{dt} = \frac{t}{s + 1}
\][/tex]

Given that [tex]\( s = 1 \)[/tex] when [tex]\( t = 0 \)[/tex]


Sagot :

Sure, let's solve the differential equation step by step. The equation is:

[tex]\[ \frac{(2t^2 + 3t)}{(2s + s)} \frac{ds}{dt} = \frac{t}{s+1} \][/tex]

First, let's simplify the equation. Note that [tex]\(2s + s = 3s\)[/tex], so the equation becomes:

[tex]\[ \frac{2t^2 + 3t}{3s} \frac{ds}{dt} = \frac{t}{s+1} \][/tex]

Now, we can separate variables. Multiply both sides by [tex]\(3s(s+1)\)[/tex] to get:

[tex]\[ (2t^2 + 3t) \, ds = 3s \cdot t \, dt \][/tex]

Now we can integrate both sides separately. Rewrite the equation in a separated form:

[tex]\[ \int \frac{3s}{2t^2 + 3t} \, ds = \int t(s+1) \, dt \][/tex]

We need to solve these integrals:

### Left Integral:
Let's integrate the left side with respect to [tex]\(s\)[/tex]:

[tex]\[ \int \frac{3s}{2t^2 + 3t} \, ds \][/tex]

### Right Integral:
For the right side, we integrate with respect to [tex]\(t\)[/tex]:

[tex]\[ \int t(s+1) \, dt \][/tex]

Let's focus on integrating these properly.

### Simplify by separable variables:
Separate and integrate as follows:

[tex]\[ \int \frac{1}{s} \, ds = \int \frac{t}{2t^2 + 3t} \, dt + \int \frac{1}{2t^2 + 3t} \, dt \][/tex]

For the simplicity purpose, we need to look at the integrals:

[tex]\[ \int \frac{1}{s} \, ds = \ln|s| + C_1 \][/tex]

Similarly, rewrite the integral on the right-hand side by separating as follows:

[tex]\[ \int \left( \frac{t}{2t^2 + 3t} + \frac{1}{2t^2 + 3t} \right) \, dt \][/tex]

We notice that the first integral can be solved by direct observation and use of logarithm properties:

### Integrate with partial fraction decomposition:

[tex]\[ \int t \left( \frac{1}{t(2t + 3)} \right) \, dt + \int \left( \frac{1}{2t(t + \frac{3}{2})} \right) \, dt \][/tex]

Hence the right-hand integral becomes:

### Substitution on left integral:
Using u-substitution where [tex]\(u = 2t^2+3t \)[/tex]:

[tex]\[ \int \frac t{u} du = \frac{\ln|u|}{2} \][/tex]

Integrate right-hand...

So, combining all:

[tex]\(\ln|s| = \frac{\ln|2t^2+ 3t|}{2} \)[/tex]

Solving the equation, we get

[tex]\(\boxed{s(t)} = e^{\frac{\ln|u|}{2}}}= \sqrt{u}} Boundary conditionsir \(|u | = |2t^2+3t|\)[/tex]

Hence \(\sqrt(u) }= sqrt(2t^3+ 3t

With constant `C`
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