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Q. For a complex number `z` ,```|z-1|+|z+1| = 2` Then `z` lies on a A) parabola B)...

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user8235304 | Student, Grade 11 | Valedictorian

Posted August 18, 2013 at 11:33 AM via web

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Q. For a complex number `z` ,```|z-1|+|z+1| = 2` Then `z` lies on a

A) parabola

B) line segment

C) circle

D) none of these

Tagged with complex numbers, math

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sciencesolve | Teacher | (Level 3) Educator Emeritus

Posted August 18, 2013 at 12:02 PM (Answer #1)

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You need to use the following identity, such that:

`|z - z_1| + |z - z_2| = c`

`z_1,z_2` represent two arbitrary fixed complex numbers

`c` represents a real number

You also should notice that the shape depends on the following triangle inequality `|z_1| + |z_2| > |z_1 - z_2|` and the following relations, such that: `c<|z_1 - z_2|, c=|z_1 - z_2|,c>|z_1 - z_2|` .

Identifying `z_1 = 1,z_2 = -1` and `c = 2` yields:

`|z_1 - z_2| = c => |1 - (-1)| = |1 + 1| = |2| = 2 = c`

Since the problem provides the relation `|z - 1| + |z + 1| = 2` and `|z_1 - z_2| = |2| = 2 = c` yields that z lies on a line segment that connects `z_1 = 1` and `z_2 = -1` .

Hence, evaluating the answer you need to select, yields that B) line segment is the valid answer.

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