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Question 1
Guide question E2.1
The equations x + y = 9 and x − y = 3 have solution (x, y). Find y.
Enter an integer, decimal or fraction without units. Use up to 5 characters, or 6 including a leading minus.
Why this answer
3.
Graphing the equations gives the intersection (6, 3). The requested quantity is the second coordinate, 3. Algebra provides a quick alternative: subtract the second equation from the first to get 2y = 6. Both original equations then hold: 6 + 3 = 9 and 6 − 3 = 3. Review Example 2.02.
The circle (x + 1)2 + (y − 2)2 = 25 intersects the line y = 5. Find the greater x-coordinate of an intersection.
Enter an integer, decimal or fraction without units. Use up to 5 characters, or 6 including a leading minus.
Why this answer
3.
Substitute y = 5:(x + 1)2 + 9 = 25, so (x + 1)2= 16. Thus x = −5 or x = 3, and the greater is 3. Graphing the circle and horizontal line gives the same pair of points, (−5, 5) and (3, 5). Both intersections lie within a natural window around center (−1, 2) with radius 5. Review Example 2.07.
For which value of k does y = k intersect y = x2 − 8x + 21 at exactly one point?
Enter an integer, decimal or fraction without units. Use up to 5 characters, or 6 including a leading minus.
Why this answer
5.
Complete the square: x2 − 8x + 21 = (x − 4)2 + 5. The parabola opens upward and has minimum output 5. A horizontal line at that minimum touches it once, at (4, 5). Values above 5 produce two intersections and values below 5 produce none. Review Example 2.12.
Write your complete response before opening the model answer. Compare both your answer and your reasoning.
Guide question E2.2
What is the greater solution of x2 − 7x + 10 = 0? Describe which graph feature represents it.
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5.
The graph y = x2 − 7x + 10 has x-intercepts 2 and 5. The greater input is 5. Factoring gives (x − 2)(x − 5) = 0, confirming both roots and their ordering. The vertex is not the solution feature requested here; a root is an input where the output equals zero. Review Example 2.03.
Guide question E2.4
Solve = x − 3 over the real numbers. Explain why a squared equation alone is insufficient.
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6.
The original right side must be nonnegative, so x ≥ 3. Squaring gives x +3 = x2 −6x +9, or (x −1)(x −6) = 0. The candidate 1 fails the original equation because 2 ≠ −2; the candidate 6 works because 3 = 3. The only solution is 6. Review Example 2.11.