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If the graph of the function x=y^2–9 on the xy-coordinate plane intersects line l at points A and B, what is the greatest possible slope of line l?

(1) Point A has coordinates (0,a)
(2) Point B has coordinates (7,b)

Kudos for a correct solution.

VERITAS PREP OFFICIAL SOLUTION:

Correct answer: (C)

Solution: We will have sufficient information if we can account for all possible variations in line 1. To determine the slope, we need two sets of coordinate points. Slope is defined by the following formula: \(\frac{(y_2−y_1)}{(x_2−x_1)}\)
Each statement by itself is insufficient. Statement (1) tells us about the coordinates of Point A, but nothing about the coordinates of Point B. And Statement (2) tells us about the coordinates of Point B, but nothing about the coordinates of Point A. However, when the two statements are combined, we can determine the greatest possible slope of line l.

Where two lines intersect, their coordinates are identical, and their equations are equal to each other. So each of the two points given in Statements 1 and 2 must satisfy the function x=y^2–9. Plugging the coordinate values of Point A into the equation, we get 0=a^2–9. Solving for a, we get that a is equal to 3 or -3. Thus, the possible coordinates of Point A are (0, 3) and (0,-3). Plugging the coordinates of Point B into the equation, we get 7=b^2–9. Solving for b, we get that b is equal to 4 or -4. Thus, the possible coordinates of Point B are (7, 4) and (7, -4).

Given these coordinate options for points A and B, there are four possible forms line 1 could take. With this information, we can determine which of the four possible slopes yields the greatest value. However, there is no need to actually calculate which line has the greatest slope.

Hi,

This question seems little clumsy to me. Whether answer cant be provided without looking either the option A and B? Whether the maximum slope of any generic line that is intersecting with a hyperbola at its points A and B would not be tan(90-degree) ?
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Hi chetan2u KarishmaB

The given equation is the equation of a parabola cutting the y-axis at (0,3) and (0,-3). If we consider the first statement, the point (0,a) lies somewhere on the y axis. Now for line l to have the maximum slope, and for it to intersect the parabola at point A and B, we can take the case when, in line "l", (0,a) = (0,3) = pt. A and pt. B = (0,-3). So this tells us that the line "l" is the y-axis. Slope = tan 90 = infinite = max. slope.
If we go by this, A can be sufficient.
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<quote option=""Bunuel"">If the graph of the function x=y^2–9 on the xy-coordinate plane intersects line l at points A and B, what is the greatest possible slope of line l?<br />
<br />
(1) Point A has coordinates (0,a)<br />
(2) Point B has coordinates (7,b)</quote>­

Bunuel can you please add the bracket to y^2?­
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<quote option=""Bunuel"">If the graph of the function x=y^2–9 on the xy-coordinate plane intersects line l at points A and B, what is the greatest possible slope of line l?<br />
<br />
(1) Point A has coordinates (0,a)<br />
(2) Point B has coordinates (7,b)</quote>­

Bunuel can you please add the bracket to y^2?­
­y^2 – 9 can only mean (y^2) – 9. If it were y^(2 – 9) it would have been written that way.
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Bunuel

Purnank
<quote option=""Bunuel"">If the graph of the function x=y^2–9 on the xy-coordinate plane intersects line l at points A and B, what is the greatest possible slope of line l?<br />
<br />
(1) Point A has coordinates (0,a)<br />
(2) Point B has coordinates (7,b)</quote>­

Bunuel can you please add the bracket to y^2?­
­y^2 – 9 can only mean (y^2) – 9. If it were y^(2 – 9) it would have been written that way.
­I got confused there :D
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If the graph of the function x=y^2–9 on the xy-coordinate plane intersects line l at points A and B, what is the greatest possible slope of line l?

(1) Point A has coordinates (0,a)
The function is such that the curve intersects y-axis at y = +5/-5 when x = 0 and x-axis at y = 0 when x = -9. 

This just gives x = 0 and y = a where a can be +/-. 
Also, the point B is necessary to know the slope of the line l.

INSUFFICIENT.

(2) Point B has coordinates (7,b)
This just gives x = 7 and y = b where b can be +/-. 
Also, the point A is necessary to know the slope of the line l.

INSUFFICIENT.

Together 1 and 2.
Both statements give solutions for a(+3/-3) using St. 1 and b(+4/-4)
Hence line l intersect at A(0,3 ; 0-3) and B(7,4 ; 7,-4).
Using these four points four slopes are possible among which greastest slope can be found.

Answer C.
 
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Hi Experts

The way the question is written i got confused and interpreted that question says as follow
f(x)=y^2-9

however its just a polynomial equation with the variable as 'Y', and can be interpreted as x=y^2-9

Can you please resolve my doubt so it wont occur in future. Thanks in advance.
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