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Complex Numbers question

2016 · 9 Apr · Shift 1 · Q28
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Complex Numbers question

2016 · 9 Apr · Shift 1 · Q28

JEE MainMathematicsComplex NumbersMCQ+4 / −1
The point represented by 2 + i in the Argand plane moves 1 unit eastwards, then 2 units northwards and finally from there 222\sqrt 222​ units in the south-westwardsdirection. Then its new position in the Argand plane is at the point represented by :
  1. A
    2 + 2i
  2. B
    1 + i
  3. C
    −-− 1 −-− i
  4. D
    −-− 2 −-− 2i
View written solutionFree

Correct answer: B

  1. Initial point in Argand plane

    The complex number 2+i2+i2+i represents the point (2,1)(2,1)(2,1) where the real part is the xxx-coordinate and the imaginary part is the yyy-coordinate.

  2. Move 1 unit eastwards

    East means positive xxx-direction.

    New point: (2,1)→(3,1)(2,1) \to (3,1)(2,1)→(3,1)

  3. Move 2 units northwards

    North means positive yyy-direction.

    New point: (3,1)→(3,3)(3,1) \to (3,3)(3,1)→(3,3)

  4. Move 222\sqrt{2}22​ units south-westwards

    South-west means equally towards south and west, i.e. along direction (−1,−1)(-1,-1)(−1,−1).

    A displacement of magnitude 222\sqrt{2}22​ in this direction has components: (−12⋅22, −12⋅22)=(−2,−2)\left(-\frac{1}{\sqrt{2}}\cdot 2\sqrt{2},\,-\frac{1}{\sqrt{2}}\cdot 2\sqrt{2}\right)=(-2,-2)(−2​1​⋅22​,−2​1​⋅22​)=(−2,−2)

    So the point becomes: (3,3)→(3−2,3−2)=(1,1)(3,3) \to (3-2,3-2)=(1,1)(3,3)→(3−2,3−2)=(1,1)

  5. Convert back to complex number

    The point (1,1)(1,1)(1,1) corresponds to 1+i1+i1+i

  6. Check options

    • A: 2+2i2+2i2+2i ❌
    • B: 1+i1+i1+i ✅
    • C: −1−i-1-i−1−i ❌
    • D: −2−2i-2-2i−2−2i ❌

Therefore, the new position is 1+i1+i1+i.

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