Balbharti 12th Maharashtra State Board Maths Solutions Book Pdf Chapter 6 Differential Equations Ex 6.1 Questions and Answers.

## Maharashtra State Board 12th Maths Solutions Chapter 6 Differential Equations Ex 6.1

1. Determine the order and degree of each of the following differential equations:

Question (i).

\(\frac{d y}{d x^{2}}+X\left(\frac{d y}{d x}\right)+y=2 \sin x\)

Solution:

The given D.E. is \(\frac{d y}{d x^{2}}+X\left(\frac{d y}{d x}\right)+y=2 \sin x\)

This D.E. has highest order derivative \(\frac{d^{2} y}{d x^{2}}\) with power 1.

∴ the given D.E. is of order 2 and degree 1.

Question (ii).

\(\sqrt[3]{1+\left(\frac{d y}{d x}\right)^{2}}=\frac{d^{2} y}{d x^{2}}\)

Solution:

The given D.E. is \(\sqrt[3]{1+\left(\frac{d y}{d x}\right)^{2}}=\frac{d^{2} y}{d x^{2}}\)

On cubing both sides, we get

\(1+\left(\frac{d y}{d x}\right)^{2}=\left(\frac{d^{2} y}{d x^{2}}\right)^{3}\)

This D.E. has highest order derivative \(\frac{d^{2} y}{d x^{2}}\) with power 3.

∴ the given D.E. is of order 2 and degree 3.

Question (iii).

\(\frac{d y}{d x}=\frac{2 \sin x+3}{\frac{d y}{d x}}\)

Solution:

The given D.E. is \(\frac{d y}{d x}=\frac{2 \sin x+3}{\frac{d y}{d x}}\)

∴ \(\left(\frac{d y}{d x}\right)^{2}\) = 2 sin x + 3

This D.E. has highest order derivative \(\frac{d y}{d x}\) with power 2.

∴ the given D.E. is of order 1 and degree 2.

Question (iv).

\(\frac{d^{2} y}{d x^{2}}+\frac{d y}{d x}+x=\sqrt{1+\frac{d^{3} y}{d x^{3}}}\)

Solution:

The given D.E. is \(\frac{d^{2} y}{d x^{2}}+\frac{d y}{d x}+x=\sqrt{1+\frac{d^{3} y}{d x^{3}}}\)

On squaring both sides, we get

\(\left(\frac{d^{2} y}{d x^{2}}+\frac{d y}{d x}+x\right)^{2}=1+\frac{d^{3} y}{d x^{3}}\)

This D.E. has highest order derivative \(\frac{d^{3} y}{d x^{3}}\) with power 1.

∴ the given D.E. has order 3 and degree 1.

Question (v).

\(\frac{d^{2} y}{d t^{2}}+\left(\frac{d y}{d t}\right)^{2}+7 x+5=0\)

Solution:

The given D.E. is \(\frac{d^{2} y}{d t^{2}}+\left(\frac{d y}{d t}\right)^{2}+7 x+5=0\)

This D.E. has highest order derivative \(\frac{d^{2} y}{d x^{2}}\) with power 1.

∴ the given D.E. has order 2 and degree 1.

Question (vi).

(y”‘)2 + 3y” + 3xy’ + 5y = 0

Solution:

The given D.E. is (y”‘)2 + 3y” + 3xy’ + 5y = 0

This can be written as:

\(\left(\frac{d^{3} y}{d x^{3}}\right)^{2}+3 \frac{d^{2} y}{d x^{2}}+3 x \frac{d y}{d x}+5 y=0\)

This D.E. has highest order derivative \(\frac{d^{3} y}{d x^{3}}\) with power 2.

∴ The given D.E. has order 3 and degree 2.

Question (vii).

\(\left(\frac{d^{2} y}{d x^{2}}\right)^{2}+\cos \left(\frac{d y}{d x}\right)=0\)

Solution:

The given D.E. is \(\left(\frac{d^{2} y}{d x^{2}}\right)^{2}+\cos \left(\frac{d y}{d x}\right)=0\)

This D.E. has highest order derivative \(\frac{d^{2} y}{d x^{2}}\)

∴ order = 2

Since this D.E. cannot be expressed as a polynomial in differential coefficients, the degree is not defined.

Question (viii).

\(\left[1+\left(\frac{d y}{d x}\right)^{2}\right]^{\frac{3}{2}}=8 \frac{d^{2} y}{d x^{2}}\)

Solution:

The given D.E. is \(\left[1+\left(\frac{d y}{d x}\right)^{2}\right]^{\frac{3}{2}}=8 \frac{d^{2} y}{d x^{2}}\)

On squaring both sides, we get

\(\left[1+\left(\frac{d y}{d x}\right)^{2}\right]^{3}=8^{2} \cdot\left(\frac{d^{2} y}{d x^{2}}\right)^{2}\)

This D.E. has highest order derivative \(\frac{d^{2} y}{d x^{2}}\) with power 2.

∴ the given D.E. has order 2 and degree 2.

Question (ix).

\(\left(\frac{d^{3} y}{d x^{3}}\right)^{\frac{1}{2}} \cdot\left(\frac{d y}{d x}\right)^{\frac{1}{3}}=20\)

Solution:

The given D.E. is \(\left(\frac{d^{3} y}{d x^{3}}\right)^{\frac{1}{2}} \cdot\left(\frac{d y}{d x}\right)^{\frac{1}{3}}=20\)

∴ \(\left(\frac{d^{3} y}{d x^{3}}\right)^{3} \cdot\left(\frac{d y}{d x}\right)^{2}=20^{6}\)

This D.E. has highest order derivative \(\frac{d^{3} y}{d x^{3}}\) with power 3.

∴ the given D.E. has order 3 and degree 3.

Question (x).

\(x+\frac{d^{2} y}{d x^{2}}=\sqrt{1+\left(\frac{d^{2} y}{d x^{2}}\right)^{2}}\)

Solution:

The given D.E. is \(x+\frac{d^{2} y}{d x^{2}}=\sqrt{1+\left(\frac{d^{2} y}{d x^{2}}\right)^{2}}\)

On squaring both sides, we get

This D.E. has highest order derivative \(\frac{d^{2} y}{d x^{2}}\) with power 1.

∴ the given D.E. has order 2 and degree 1.