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Range (Posted on 2021-09-20) Difficulty: 2 of 5
Let x, y are real numbers such that x2+2cos(y)=1. Find the range of x-cos(y).

No Solution Yet Submitted by Danish Ahmed Khan    
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Solution solution | Comment 1 of 4
Since y = arccos((1-x^2)/2), y has an imaginary component if 

(1-x^2)/2 < -1
1-x^2 < -2
3 < x^2

y is real if -sqrt(3) <= x <= sqrt(3)

x = -1 falls within this range and is the absolute minimum of x-(1-x^2)/2 which is -1, the vertex of a concave up parabola.

At x=sqrt(3), x-(1-x^2)/2 reaches its maximum within the allotted domain, 1 + sqrt(3).


-1 to 1+sqrt(3) is the range.

  Posted by Charlie on 2021-09-20 10:21:05
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