A data sufficiency question in coordinate geometry
Does the line x + y = 6 intersect or touch circle C with radius 5 units?
1. Center of the circle lies in the third quadrant.
2. Point (-4, -4) does not lie inside the circle.
Correct Answer is Choice E. The data is INSUFFICIENT.
Explanatory Answer
The line will intersect or touch the circle if the distance between the center of the circle and any point on the line is less than or equal to the radius of the circle.
Let us a pick a point on the line - say A(3, 3).
Statement 1: The center of the circle lies in the third quadrant.
The center could be at O
1(-0.5, -0.5) or could be at O
2(-10, -10).
Case 1: If the center is at O
1(-0.5, -0.5), then the distance between O
1A is less than 5 units, the radius of the circle. So, the line will intersect with the circle.
Case 2: On the other hand if the center is at O
2(-10, -10), then the distance between O
2A will be greater than 5 units, the radius of the circle. So, the line will neither touch nor intersect with the circle.
Hence, from statement 1 we cannot answer the question. Data INSUFFICIENT.
Statement 2: Point (-4, -4) does not lie inside the circle.
The distance between the center of the circle and (-4, -4) is more than 5 units.
Case 1: The center of the circle could be at (0, 0) and point (-4, -4) will lie outside the circle. However, the distance between the center and point A(3, 3) is less than 5 units. Hence, the line will intersect with the circle.
Case 2: Conversely, the center of the circle could be at (-10, -10). Point (-4, -4) will still lie outside the circle and the distance between point A(3,3 ) and the center (-10, -10) will be more than 5 units. Hence, the line will neither touch nor intersect with the circle.
Hence, from statement 2 we cannot answer the question. Data INSUFFICIENT.
Combining the two statements - Center of the circle lies in the third quadrant and Point (-4, -4) does not lie inside the circle.
Consider the two following options for the center of the circle.
The center could be at O
1(-0.1, -0.1) or could be at O
2(-10, -10).
Case 1: The distance between O
1(-0.1, -0.1) and (-4, -4) is more than 5 units and that between O
1(-0.1, -0.1) and (3, 3) is less than 5 units. Hence, all conditions stated in the two statements are satisfied and the line intersects with the circle.
Case 2: The distance between O
2(-10, -10) and (-4, -4) is more than 5 units and that between O
2(-10, -10) and (3, 3) is also more than 5 units. Hence, all conditions stated in
the two statements are satisfied - but the line does not intersect or touch the circle.
Therefore, using the statements independently or together we will not be able to answer the question.
Choice E is the answer.