Consider the region S of complex number a such that ∣ z 2 + a z + 1 ∣ = 1 , where complex number z is on the locus ∣ z ∣ = 1 . If A denotes the area of S in the Argand plane, find ⌊ 2 A ⌋ .
Notations:
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U can also simplify like this
∣ z ∣ = 1 ⟹ ∣ z ∣ 2 = 1 .Now ∣ z 2 + a z + 1 ∣ = 1 ⟹ ∣ z 2 + a z + ∣ z ∣ 2 ∣ = 1 ⟹ ∣ z 2 + a z + z z ∣ = 1 ⟹ ∣ z ∣ ∣ z + z + a ∣ = 1 .
We can cosider z = cos θ + i sin θ so z + z = 2 cos θ .
∣ 2 cos θ + a ∣ = 1 and then ur solution.
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yes .exactly the way i approached .
Whoa!! Nice approach! I did it the long way
How you got this figure.. ?
It seems that this question would have n solvers n likes
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Let us denote z as c o s ( θ ) + j ⋅ s i n ( θ ) and a as x + j y
∣ z 2 + a z + 1 ∣ = 1
∣ c o s ( 2 θ ) + j s i n ( 2 θ ) + ( x c o s ( θ ) − y s i n ( θ ) ) + j ( x s i n ( θ ) + y c o s ( θ ) ) + 1 ∣ = 1
( c o s ( 2 θ ) + ( x c o s ( θ ) − y s i n ( θ ) ) + 1 ) 2 + ( x s i n ( θ ) + y c o s ( θ ) + s i n ( 2 θ ) ) 2 = 1
( 2 c o s 2 ( θ ) + x c o s ( θ ) − y s i n ( θ ) ) 2 + ( x s i n ( θ ) + y c o s ( θ ) + 2 s i n ( θ ) c o s ( θ ) ) 2 = 1
x 2 + y 2 + 4 c o s 2 ( θ ) + 4 x c o s ( θ ) = 1
( x + 2 c o s ( θ ) ) 2 + y 2 = 1
Since 2 c o s ( θ ) varies from − 2 to 2 , the figure is equivalent to a circle with center with y coordinate equal to 0 and x coordinate varying from − 2 to 2 , which means a figure like:
Which means that the area will be a rectangle of base 4 and height 2 plus 2 semi-circles (1 circle) of radius equal to 1 . Or:
A = 4 ⋅ 2 + π ⋅ 1 2
A = 8 + π = 1 1 . 1 4 1 6 . . .
Then ⌊ 2 A ⌋ = 5