Complex equation(A JEE Problem)!

Algebra Level 3

Let z = x + i y z=x+iy be a complex number where x x and y y are integers. Find the area of the rectangle whose vertices are the roots of the equation: z z ˉ 3 + z ˉ z 3 = 350 \large\ z\bar{z}^3 + \bar{z} z^3=350

80 40 32 48

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1 solution

Chan Tin Ping
Nov 4, 2017

z z ˉ 3 + z ˉ z 3 = 350 z z ˉ ( z ˉ 2 + z 2 ) = 350 ( x 2 + y 2 ) ( x 2 2 x y i y 2 + x 2 + 2 x y i y 2 ) = 350 ( x 2 + y 2 ) ( 2 ( x 2 y 2 ) ) = 350 ( x 2 y 2 ) ( x 2 + y 2 ) = 175 \begin{aligned} z\bar{z}^3+ \bar{z}z^3&=350 \\ z \bar{z}(\bar{z}^2+z^2)&=350 \\ (x^2+y^2)(x^2-2xyi-y^2+x^2+2xyi-y^2)&=350 \\ (x^2+y^2)(2(x^2-y^2)) &=350 \\ (x^2-y^2)(x^2+y^2) &=175 \end{aligned}

Factorizes 175, we got 175=5^2 × 7. Hence, 175=1×175=5×35=25×7. As x^2 & y^2 are square integers, the only factorization of 175 must be 25×7. (If 175 = a × b 175=a\times b ), then x 2 = a + b 2 x^2=\frac{a+b} {2} and y 2 = a b 2 ^2=\frac{a-b} {2} )

Hence, x = ± 4 x=\pm4 and y = ± 3 y=\pm3 , so the area is 8 × 6 = 48 8 \times 6 = 48 .

Nice solution!(upvoted) :)

Rishu Jaar - 3 years, 7 months ago

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Thanks :):):):):):)

Chan Tin Ping - 3 years, 7 months ago

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Can you check this one please sir , my friends and me are a bit confused. https://brilliant.org/problems/vectors1/

Rishu Jaar - 3 years, 7 months ago

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