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MathsHardMCQ2019 · 12 Jan Shift 1

Q71.If a variable line 3x + 4y −λ = 0 is such that the two circles x2 + y2 −2x −2y + 1 = 0 and x2 + y2 −18x −2y + 78 = 0 are on its opposite sides, then the set of all values of λ is the interval : (1) [13, 23] (2) (23, 31) (3) [12, 21] (4) (2, 17)

What This Question Tests

This question tests the concept of determining whether two points (or in this case, centers of circles) lie on opposite sides of a line. For two points to be on opposite sides of the line ax+by+c=0, the values of ax+by+c when substituting the coordinates of the points must have opposite signs. Determine the centers of the two circles and apply this condition to find the range of λ.

Concepts Tested

Position of a point relative to a linePosition of a circle relative to a line

Formulas Used

Equation of circle (x-h)^2 + (y-k)^2 = r^2

Sign of L(x,y) for a point (x,y) relative to line L=0

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