collection of tough problems from G PREP - 15

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Circle C and line K lie in the xy plane. If circle C is centered at the origin and has radius 1 , does line K intersect circle C??

(1) The x intercept of line k is greater than 1

(2) The slope of line K is -1/10
Source: — Data Sufficiency |

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by harsh.champ » Sat Feb 06, 2010 6:16 am
abhasjha wrote:Circle C and line K lie in the xy plane. If circle C is centered at the origin and has radius 1 , does line K intersect circle C??

(1) The x intercept of line k is greater than 1

(2) The slope of line K is -1/10
Basic rule 1:A line can intersect at maximum 2 points.
Basic rule 2:A unique line equation can be found by knowing 2 variables(the slope and the intercept)

Hence,C.

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by ajith » Sat Feb 06, 2010 8:29 am
abhasjha wrote:Circle C and line K lie in the xy plane. If circle C is centered at the origin and has radius 1 , does line K intersect circle C??

(1) The x intercept of line k is greater than 1

(2) The slope of line K is -1/10
1.) The x intercept of line k is greater than 1; x intercept is greater than one but this doesnt assure the line intersects the circle or not

2) slope is -1/10 is insufficient to conclude whether the line intersects the circle

combining 1&2 we can derive the equation of the line and check whether the circle is intersected by the line
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by abhasjha » Mon Feb 08, 2010 12:28 am
OA - E

just draw a circle with the center at 0,0... with a radius of 1 the circle will touch (0,1) (1,0) (0,-1) & (-1,0)

Statement (1) tells you that line K (and i'm pretty sure that yes you imagine it's infinite because it would be called line segment k something not line k) has an x-intercept greater than 1... on your diagram this would be to the right of the point (1,0) you have the circle touching... since you have no idea how far right this point is, it could be at (5000,0) or (2,0) and you have no idea what the slope is, it could be a vertical line like x=5000 or x=2 and never touch the circle, or a regular positive or negative slope. Not sufficient

Statement (2) tells you that the slope of line k is -1/10... this tells you absolutley nothing about the placement of the line in relation of the circle... not sufficient

Together imagine the two examples I gave for possible places of line k on the x-axis... If line K's x-intercept was at (2,0) with a slope of -1/10 it would run right into the circle as it is 1 unit away and hit the y-axis at (0,1/5) (in the circle)... now imagine the line K hits the x-axis at (5000,0) all the way to the right of the circle with a slope of -1/10 it would run all the way back to the y-axis and touch it at (0,500) way above the circle...

therefore the answer is E