The equation of the line tangent to a curve at a point. 70 problems with worked solutions; in 70 of them every
equation is proved by a computer algebra system.
20 worked problems
Try each one before opening the solution. Every line is labeled with what checked it. How we verify
The graph of y = 2x + sin(x) near x = pi. A secant line through the point (pi, 2pi) and a second point on the curve turns into the tangent line as the second point slides in; its slope settles at 1, giving y = x + pi.
✓ Nihil obstat Lines: 3 proved, 2 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
\[ \left(5 x - 10\right) e^{4} + 2 e^{4} = 5 x e^{4} - 8 e^{4} \]
Point-slope form, then simplify.✓ Proved
Answer \( y = 5 x e^{4} - 8 e^{4} \)
The graph of y = x·e^(2x) near x = 2. A secant line through the point (2, 2e^(4)) and a second point on the curve turns into the tangent line as the second point slides in; its slope settles at 5e^(4), giving y = 5x·e^(4) - 8e^(4).
✓ Nihil obstat Lines: 4 proved, 1 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 graph of y = -x - 2sin(x) + 2 near x = pi. A secant line through the point (pi, 2 - pi) and a second point on the curve turns into the tangent line as the second point slides in; its slope settles at 1, giving y = x - 2pi + 2.
✓ Nihil obstat Lines: 3 proved, 2 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 graph of y = x·e^(-x) near x = -1. A secant line through the point (-1, -E) and a second point on the curve turns into the tangent line as the second point slides in; its slope settles at 2E, giving y = 2E·x + E.
✓ Nihil obstat Lines: 4 proved, 1 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
Answer \( y = - \frac{x}{e^{2}} - \frac{2}{e^{2}} \)
The graph of y = x·e^(2x) near x = -1. A secant line through the point (-1, -e^(-2)) and a second point on the curve turns into the tangent line as the second point slides in; its slope settles at -e^(-2), giving y = -x·e^(-2) - 2e^(-2).
✓ Nihil obstat Lines: 4 proved, 1 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 graph of y = -2x² + x + 3 - 3/x near x = -1. A secant line through the point (-1, 3) and a second point on the curve turns into the tangent line as the second point slides in; its slope settles at 8, giving y = 8x + 11.
✓ Nihil obstat Lines: 3 proved, 2 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
\[ \left(3 x + 3\right) e^{2} - e^{2} = 3 x e^{2} + 2 e^{2} \]
Point-slope form, then simplify.✓ Proved
Answer \( y = 3 x e^{2} + 2 e^{2} \)
The graph of y = x·e^(-2x) near x = -1. A secant line through the point (-1, -e^(2)) and a second point on the curve turns into the tangent line as the second point slides in; its slope settles at 3e^(2), giving y = 3x·e^(2) + 2e^(2).
✓ Nihil obstat Lines: 4 proved, 1 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 graph of y = -x + 3sin(x) near x = pi. A secant line through the point (pi, -pi) and a second point on the curve turns into the tangent line as the second point slides in; its slope settles at -4, giving y = -4x + 3pi.
✓ Nihil obstat Lines: 3 proved, 2 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 graph of y = -x² - 2x - 4 - 3/x near x = 2. A secant line through the point (2, -27/2) and a second point on the curve turns into the tangent line as the second point slides in; its slope settles at -21/4, giving y = -21x/4 - 3.
✓ Nihil obstat Lines: 3 proved, 2 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 graph of y = 3x² - 3x + 2 + 2/x near x = -1. A secant line through the point (-1, 6) and a second point on the curve turns into the tangent line as the second point slides in; its slope settles at -11, giving y = -11x - 5.
✓ Nihil obstat Lines: 3 proved, 2 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
\[ \left(5 x - 20\right) e^{4} + 4 e^{4} = 5 x e^{4} - 16 e^{4} \]
Point-slope form, then simplify.✓ Proved
Answer \( y = 5 x e^{4} - 16 e^{4} \)
The graph of y = x·e^(x) near x = 4. A secant line through the point (4, 4e^(4)) and a second point on the curve turns into the tangent line as the second point slides in; its slope settles at 5e^(4), giving y = 5x·e^(4) - 16e^(4).
✓ Nihil obstat Lines: 4 proved, 1 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
Answer \( y = - \frac{3 x}{e^{4}} + \frac{8}{e^{4}} \)
The graph of y = x·e^(-2x) near x = 2. A secant line through the point (2, 2e^(-4)) and a second point on the curve turns into the tangent line as the second point slides in; its slope settles at -3e^(-4), giving y = -3x·e^(-4) + 8e^(-4).
✓ Nihil obstat Lines: 4 proved, 1 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 graph of y = sqrt(x) - x + 3 near x = 1. A secant line through the point (1, 3) and a second point on the curve turns into the tangent line as the second point slides in; its slope settles at -1/2, giving y = 7/2 - x/2.
✓ Nihil obstat Lines: 3 proved, 2 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 graph of y = -x² + 4x + 3 + 3/x near x = 1. A secant line through the point (1, 9) and a second point on the curve turns into the tangent line as the second point slides in; its slope settles at -1, giving y = 10 - x.
✓ Nihil obstat Lines: 3 proved, 2 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 graph of y = x + 3sin(x) + 2 near x = 0. A secant line through the point (0, 2) and a second point on the curve turns into the tangent line as the second point slides in; its slope settles at 4, giving y = 4x + 2.
✓ Nihil obstat Lines: 3 proved, 2 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 graph of y = 2sqrt(x) + x - 1 near x = 4. A secant line through the point (4, 7) and a second point on the curve turns into the tangent line as the second point slides in; its slope settles at 3/2, giving y = 3x/2 + 1.
✓ Nihil obstat Lines: 3 proved, 2 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 graph of y = sqrt(x) + x - 3 near x = 4. A secant line through the point (4, 3) and a second point on the curve turns into the tangent line as the second point slides in; its slope settles at 5/4, giving y = 5x/4 - 2.
✓ Nihil obstat Lines: 3 proved, 2 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 graph of y = -2x - sin(x) - 2 near x = pi. A secant line through the point (pi, -2pi - 2) and a second point on the curve turns into the tangent line as the second point slides in; its slope settles at -1, giving y = -x - pi - 2.
✓ Nihil obstat Lines: 3 proved, 2 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 graph of y = -3x² - x + 2 + 3/x near x = 1. A secant line through the point (1, 1) and a second point on the curve turns into the tangent line as the second point slides in; its slope settles at -10, giving y = 11 - 10x.
✓ Nihil obstat Lines: 3 proved, 2 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
Answer \( y = - \frac{x}{e^{2}} + \frac{4}{e^{2}} \)
The graph of y = x·e^(-x) near x = 2. A secant line through the point (2, 2e^(-2)) and a second point on the curve turns into the tangent line as the second point slides in; its slope settles at -e^(-2), giving y = -x·e^(-2) + 4e^(-2).
✓ Nihil obstat Lines: 4 proved, 1 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