Constant coefficients: the characteristic equation and its three cases. 70 problems with worked solutions; in 70 of them every
equation is proved by a computer algebra system.
10 worked problems
Try each one before opening the solution. Every line is labeled with what checked it. How we verify
Roots α ± βi give y = e^(αx)(C₁cos βx + C₂sin βx).
Reviewed
Use y(0) and y'(0) to find C₁ and C₂.
Reviewed
\[ \left(\frac{40 \sin{\left(3 x \right)}}{3} + 10 \cos{\left(3 x \right)}\right) e^{- x} + 2 \frac{d}{d x} \left(\frac{4 \sin{\left(3 x \right)}}{3} + \cos{\left(3 x \right)}\right) e^{- x} + \frac{d^{2}}{d x^{2}} \left(\frac{4 \sin{\left(3 x \right)}}{3} + \cos{\left(3 x \right)}\right) e^{- x} = 0 \]
The solution satisfies the equation.✓ Proved
\[ 1 \]
y(0).Reviewed
\[ 3 \]
y'(0).Reviewed
Answer \( y = \left(\frac{4 \sin{\left(3 x \right)}}{3} + \cos{\left(3 x \right)}\right) e^{- x} \)
✓ Nihil obstat Lines: 2 proved, 5 reviewed. The answer was also checked a second way, without looking at the solution. Reviewers found nothing wrong with the explanation. The full receipt ·
How we verify
Try y = e^(mx): the characteristic equation is m² + bm + c = 0.
Reviewed
\[ \left(m - 3\right)^{2} = m^{2} - 6 m + 9 \]
Roots: 3.✓ Proved
A repeated root r gives y = (C₁ + C₂x)e^(rx).
Reviewed
Use y(0) and y'(0) to find C₁ and C₂.
Reviewed
\[ \left(63 x - 27\right) e^{3 x} - 6 \frac{d}{d x} \left(7 x - 3\right) e^{3 x} + \frac{d^{2}}{d x^{2}} \left(7 x - 3\right) e^{3 x} = 0 \]
The solution satisfies the equation.✓ Proved
\[ -3 \]
y(0).Reviewed
\[ -2 \]
y'(0).Reviewed
Answer \( y = \left(7 x - 3\right) e^{3 x} \)
✓ Nihil obstat Lines: 2 proved, 5 reviewed. The answer was also checked a second way, without looking at the solution. Reviewers found nothing wrong with the explanation. The full receipt ·
How we verify
✓ Nihil obstat Lines: 2 proved, 5 reviewed. The answer was also checked a second way, without looking at the solution. Reviewers found nothing wrong with the explanation. The full receipt ·
How we verify
✓ Nihil obstat Lines: 2 proved, 5 reviewed. The answer was also checked a second way, without looking at the solution. Reviewers found nothing wrong with the explanation. The full receipt ·
How we verify
✓ Nihil obstat Lines: 2 proved, 5 reviewed. The answer was also checked a second way, without looking at the solution. Reviewers found nothing wrong with the explanation. The full receipt ·
How we verify
Roots α ± βi give y = e^(αx)(C₁cos βx + C₂sin βx).
Reviewed
Use y(0) and y'(0) to find C₁ and C₂.
Reviewed
\[ \left(- 5 \sin{\left(2 x \right)} - 10 \cos{\left(2 x \right)}\right) e^{- x} + 2 \frac{d}{d x} \left(- \sin{\left(2 x \right)} - 2 \cos{\left(2 x \right)}\right) e^{- x} + \frac{d^{2}}{d x^{2}} \left(- \sin{\left(2 x \right)} - 2 \cos{\left(2 x \right)}\right) e^{- x} = 0 \]
The solution satisfies the equation.✓ Proved
\[ -2 \]
y(0).Reviewed
\[ 0 \]
y'(0).Reviewed
Answer \( y = - \left(\sin{\left(2 x \right)} + 2 \cos{\left(2 x \right)}\right) e^{- x} \)
✓ Nihil obstat Lines: 2 proved, 5 reviewed. The answer was also checked a second way, without looking at the solution. Reviewers found nothing wrong with the explanation. The full receipt ·
How we verify
Try y = e^(mx): the characteristic equation is m² + bm + c = 0.
Reviewed
\[ \left(m - 2\right)^{2} = m^{2} - 4 m + 4 \]
Roots: 2.✓ Proved
A repeated root r gives y = (C₁ + C₂x)e^(rx).
Reviewed
Use y(0) and y'(0) to find C₁ and C₂.
Reviewed
\[ \left(36 x - 12\right) e^{2 x} - 4 \frac{d}{d x} \left(9 x - 3\right) e^{2 x} + \frac{d^{2}}{d x^{2}} \left(9 x - 3\right) e^{2 x} = 0 \]
The solution satisfies the equation.✓ Proved
\[ -3 \]
y(0).Reviewed
\[ 3 \]
y'(0).Reviewed
Answer \( y = \left(9 x - 3\right) e^{2 x} \)
✓ Nihil obstat Lines: 2 proved, 5 reviewed. The answer was also checked a second way, without looking at the solution. Reviewers found nothing wrong with the explanation. The full receipt ·
How we verify
✓ Nihil obstat Lines: 2 proved, 5 reviewed. The answer was also checked a second way, without looking at the solution. Reviewers found nothing wrong with the explanation. The full receipt ·
How we verify
✓ Nihil obstat Lines: 2 proved, 5 reviewed. The answer was also checked a second way, without looking at the solution. Reviewers found nothing wrong with the explanation. The full receipt ·
How we verify
✓ Nihil obstat Lines: 2 proved, 5 reviewed. The answer was also checked a second way, without looking at the solution. Reviewers found nothing wrong with the explanation. The full receipt ·
How we verify