The integrating factor method for y′ + p(x)y = q(x). 70 problems with worked solutions; in 70 of them every
equation is proved by a computer algebra system.
11 worked problems
Try each one before opening the solution. Every line is labeled with what checked it. How we verify
The slope field of y' = -3y + e^(x): short segments showing the slope at each point. Several solution curves follow the field; the one through (0, 2) is highlighted, y = (e^(4x) + 7)·e^(-3x)/4.
✓ Nihil obstat Lines: 3 proved, 3 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
Multiplying by e^(ax) turns the left side into (e^(ax) y)'.✓ Proved
\[ \int 3 x e^{x}\, dx = \left(3 x - 3\right) e^{x} \]
Integrate the right side.✓ Proved
Setting x = 0 and y = -2 fixes the constant of integration: C = 1.
Reviewed
\[ 3 x + \frac{d}{d x} \left(3 x - 3 + e^{- x}\right) - 3 + e^{- x} = 3 x \]
The solution satisfies the equation.✓ Proved
\[ -2 \]
And the initial condition.Reviewed
Answer \( y = 3 x - 3 + e^{- x} \)
The slope field of y' = 3x - y: short segments showing the slope at each point. Several solution curves follow the field; the one through (0, -2) is highlighted, y = 3x - 3 + e^(-x).
✓ Nihil obstat Lines: 3 proved, 3 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
The slope field of y' = 1 - 4y: short segments showing the slope at each point. Several solution curves follow the field; the one through (0, 3) is highlighted, y = 1/4 + 11e^(-4x)/4.
✓ Nihil obstat Lines: 3 proved, 3 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
The slope field of y' = -2y + 2e^(-2x): short segments showing the slope at each point. Several solution curves follow the field; the one through (0, 3) is highlighted, y = (2x + 3)·e^(-2x).
✓ Nihil obstat Lines: 3 proved, 3 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
The slope field of y' = x - 2y: short segments showing the slope at each point. Several solution curves follow the field; the one through (0, 2) is highlighted, y = x/2 - 1/4 + 9e^(-2x)/4.
✓ Nihil obstat Lines: 3 proved, 3 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
Multiplying by e^(ax) turns the left side into (e^(ax) y)'.✓ Proved
\[ \int 2 x e^{x}\, dx = \left(2 x - 2\right) e^{x} \]
Integrate the right side.✓ Proved
Setting x = 0 and y = 1 fixes the constant of integration: C = 3.
Reviewed
\[ 2 x + \frac{d}{d x} \left(2 x - 2 + 3 e^{- x}\right) - 2 + 3 e^{- x} = 2 x \]
The solution satisfies the equation.✓ Proved
\[ 1 \]
And the initial condition.Reviewed
Answer \( y = 2 x - 2 + 3 e^{- x} \)
The slope field of y' = 2x - y: short segments showing the slope at each point. Several solution curves follow the field; the one through (0, 1) is highlighted, y = 2x - 2 + 3e^(-x).
✓ Nihil obstat Lines: 3 proved, 3 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
The slope field of y' = -3y + 3e^(x): short segments showing the slope at each point. Several solution curves follow the field; the one through (0, -2) is highlighted, y = (3e^(4x) - 11)·e^(-3x)/4.
✓ Nihil obstat Lines: 3 proved, 3 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
The slope field of y' = -4y + 2e^(x): short segments showing the slope at each point. Several solution curves follow the field; the one through (0, 1) is highlighted, y = (2e^(5x) + 3)·e^(-4x)/5.
✓ Nihil obstat Lines: 3 proved, 3 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
The slope field of y' = 5 - 4y: short segments showing the slope at each point. Several solution curves follow the field; the one through (0, -1) is highlighted, y = 5/4 - 9e^(-4x)/4.
✓ Nihil obstat Lines: 3 proved, 3 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
The slope field of y' = -2y + e^(-2x): short segments showing the slope at each point. Several solution curves follow the field; the one through (0, 4) is highlighted, y = (x + 4)·e^(-2x).
✓ Nihil obstat Lines: 3 proved, 3 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
The slope field of y' = -3y + e^(-3x): short segments showing the slope at each point. Several solution curves follow the field; the one through (0, -2) is highlighted, y = (x - 2)·e^(-3x).
✓ Nihil obstat Lines: 3 proved, 3 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