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.

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_{1}A 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_{2}A 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.

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

Case 1: If the center is at O

Case 2: On the other hand if the center is at O

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

Case 1: The distance between O

Case 2: The distance between O

Therefore, using the statements independently or together we will not be able to answer the question.

Choice E is the answer.

Labels: Circles, GMAT Coordinate Geometry, GMAT Data Sufficiency, GMAT DS, GMAT Geometry, Lines