Cunning complex 3

Algebra Level 4

If w 1 w\neq 1 is a cube root of unity and a + b = 1 a+b=1 , a 3 + b 3 = 1001 { a }^{ 3 }+{ b }^{ 3 }=1001 . Find the value of ( a w 2 + b w ) ( a w + b w 2 ) \left( { aw }^{ 2 }+bw \right) \left( aw+{ bw }^{ 2 } \right)

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The answer is 1001.00.

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4 solutions

Tanishq Varshney
Mar 19, 2015

( a + b ) ( a 2 a b + b 2 ) = 1001 (a+b)(a^2-ab+b^2)=1001 ................... ( 1 ) (1)

a 2 ω 3 + a b ( ω + ω 2 ) + b 2 ω 3 a^2 \omega^{3} +ab(\omega+\omega^{2})+b^2 \omega^{3}

we know that ω 3 = 1 a n d 1 + ω 2 + ω = 0 \omega^{3}=1~and ~1+\omega^{2}+\omega=0

expression reduces to a 2 a b + b 2 a^2 -ab+b^2

as in 1 1

a + b = 1 a+b=1 , thus a 2 a b + b 2 = 1001 a^2 -ab+b^2=1001

@Tanishq Varshney Thanks for the solution

Utkarsh Bansal - 6 years, 2 months ago

Good solution,but overrated question.

Ayush Verma - 6 years, 2 months ago
Saurav Pal
Mar 30, 2015

( a ω 2 + b ω ) ( a ω + b ω 2 ) = a 2 + b 2 + a b ( ω + ω 2 ) = a 2 + b 2 a b . a 3 + b 3 a + b = a 2 + b 2 a b = 1001 1 = 1001. (a{ \omega }^{ 2 }+b\omega )(a\omega +b{ \omega }^{ 2 })={ a }^{ 2 }+{ b }^{ 2 }+ab(\omega +{ \omega }^{ 2 })={ a }^{ 2 }+{ b }^{ 2 }-ab.\quad \\ \frac { { a }^{ 3 }+{ b }^{ 3 } }{ a+b } ={ a }^{ 2 }+{ b }^{ 2 }-ab=\frac { 1001 }{ 1 } =1001.

right man...... I also did it exactly the same way

Raushan Sharma - 6 years, 2 months ago

Since w^3 = 1 and w is complex and imaginary, w^2 + w + 1 = 0.

(aw^2 + bw)(aw + bw^2) = (a^2)(w^3) + ab(w^4) + ab(w^2) + (b^2)(w^3) = (a^2 + b^2) + abw + ab(w^2) = (a^2 + b^2) + ab(w + w^2) = a^2 + b^2 - ab

From the systems for a and b, a^2 - ab + b^2 = 1001.

Hence, the answer.

y is it with 335 point (level 5)?? its a level 3 question!!!

A Former Brilliant Member - 6 years, 2 months ago

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Yes Sir I agree you but I first set it to Level 3

Utkarsh Bansal - 6 years, 2 months ago
Jyotsna Sharma
Mar 26, 2015

Multiplying and dividing by w. We get (aw+b)(aw^2+b)= a^2+b^2+ab (w+w^2). This is same as (a+b)^2 -3ab=1-3(-1000/3)= 1001

+1!! use latex!!

A Former Brilliant Member - 6 years, 2 months ago

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Sorry but will take care in future

Jyotsna Sharma - 6 years, 2 months ago

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