Question
Solve the following differential equation:
$\text{x}\frac{\text{dy}}{\text{dx}}+2\text{y}=\text{x}\cos\text{x}$

Answer

Here, $\frac{\text{dy}}{\text{dx}}+\frac{2\text{y}}{\text{x}}=\cos\text{x}$

It is a linear differential equation. Comparing it with,

$\frac{\text{dy}}{\text{dx}}+\text{Py}=\text{Q}$

$\text{P}=\frac{2}{\text{x}},\text{Q}=\cos\text{x}$

I.F. $=\text{e}^{\int\text{Pdx}}$

$=\text{e}^{2\int\frac{1}{\text{x}}\text{dx}}$

$=\text{e}^{2\log|\text{x}|}$

$=\text{x}^2$

Solution of the equation is given by,

$\text{y}\times(\text{I.F.}=\int\text{Q}\times(\text{I.F.})\text{dx + C}$

$\text{y}(\text{x}^2)=\int\cos\text{x}(\text{x}^2)\text{dx + C}$

$\text{yx}^2=\int\text{x}^2\cos\text{xdx + C}$

$=\text{x}^2\int\cos\text{x}-\int(2\text{x}\times\int\cos\text{xdx})\text{dx + C}$

Usind integration by parts

$\text{yx}^2=\text{x}^2\sin\text{x}-\int2\text{x}\sin\text{xdx + C}$

$=\text{x}^2\sin\text{x}-2\big[\text{x}\times\int\sin\text{xdx}-\int(1\times\int\sin\text{xdx})\text{dx}\big]+\text{C}$

$=\text{x}^2\sin\text{x}+2\text{x}\cos\text{x}-2\int\cos\text{xdx + C}$

$\text{yx}^2=\text{x}^2\sin\text{x}+2\text{x}\cos\text{x}-2\sin\text{x + C}$

$\text{y}=\sin\text{x}+\frac{2}{\text{x}}\cos\text{x}-\frac{2}{\text{x}^2}\sin\text{x}+\frac{\text{C}}{\text{x}^2}$

Need a full question paper?

Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.

Start Generating Free

Similar questions

Prove that:
$\begin{vmatrix}\text{a}^2&\text{a}^2-(\text{b}-\text{c})^2&\text{bc}\\\text{b}^2&\text{b}^2-(\text{c}-\text{a})^2&\text{ca}\\\text{c}^2&\text{c}^2-(\text{a}-\text{b})^2&\text{ab}\end{vmatrix}$
$=(\text{a}-\text{b})(\text{b}-\text{c})(\text{c}-\text{b})(\text{a}+\text{b}+\text{c})(\text{a}^2+\text{b}^2+\text{c}^2)$
Find $\frac{\text{dy}}{\text{dx}}$ in the following cases:
x5 + y5 = 5xy
A wholesale dealer deals in two kinds, A and B (say) of mixture of nuts. Each kg of mixture A contains 60 grams of almonds, 30 grams of cashew nuts and 30 grams of hazel nuts. Each kg of mixture B contains 30 grams of almonds, 60 grams of cashew nuts and 180 grams of hazel nuts. The remainder of both mixtures is per nuts. The dealer is contemplating to use mixtures A and B to make a bag which will contain at least 240 grams of almonds, 300 grams of cashew nuts and 540 grams of hazel nuts. Mixture A costs Rs. 8 per kg. and mixture B costs Rs. 12 per kg. Assuming that mixtures A and B are uniform, use graphical method to determine the number of kg. of each mixture which he should use to minimise the cost of the bag.
Integrate the function in Exercise:

$\frac{1}{\big(\text{x}^{2}+1\big)\big(\text{x}^{2}+4\big)}$

Show that the points $2\hat{\text{i}},-\hat{\text{i}}-4\hat{\text{j}}\text{ and }-\hat{\text{i}}+4\hat{\text{j}}$ form an isosceles triangle.
Using properties of definite integrals, evaluate:

$\int\limits^{\pi/4}_{0}\text{log (1 + tan x) dx}$.

Water is running into an inverted cone at the rate of $\pi$ cubic metres per minute. The height of the cone is 10 metres, and the radius of its base is 5m. How fast the water level is rising when the water stands 7.5m below the base.
Find the area of the region enclosed between the two curve x2 + y2 = 9 and (x - 3)2 + y2 = 9.
The scalar product of the vector $\hat{\text{i}}+\hat{\text{j}}+\hat{\text{k}}$ with the unit vector along the sum of vectors $2\hat{\text{i}}+4\hat{\text{j}}-5\hat{\text{k}}$ and $\lambda\hat{\text{i}}+2\hat{\text{j}}+3\hat{\text{k}}$ is equal to one. Find the value of λ.