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Let a,b,c,ka,b,c,k be rational numbers such that kk is not a perfect cube. \newlineIf a+bk13+ck23a+bk^{\frac{1}{3}}+ck^{\frac{2}{3}} then prove that a=b=c=0a=b=c=0.

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Q. Let a,b,c,ka,b,c,k be rational numbers such that kk is not a perfect cube. \newlineIf a+bk13+ck23a+bk^{\frac{1}{3}}+ck^{\frac{2}{3}} then prove that a=b=c=0a=b=c=0.
  1. Eliminate cube root: Multiply the equation by k1/3k^{1/3} to eliminate the cube root.\newlineak1/3+bk2/3+ck=0ak^{1/3} + bk^{2/3} + ck = 0
  2. System of equations: Now we have a system of two equations:\newline11) a+bk13+ck23=0a + bk^{\frac{1}{3}} + ck^{\frac{2}{3}} = 0\newline22) ak13+bk23+ck=0ak^{\frac{1}{3}} + bk^{\frac{2}{3}} + ck = 0
  3. Subtract and simplify: Subtract the second equation from the first one multiplied by k1/3k^{1/3}:\newline(aak1/3)+(bk1/3bk)+(ck2/3ck4/3)=0(a - ak^{1/3}) + (bk^{1/3} - bk) + (ck^{2/3} - ck^{4/3}) = 0
  4. Distinct coefficients: Simplify the equation: a(1k13)+b(k13k)+c(k23k43)=0a(1 - k^{\frac{1}{3}}) + b(k^{\frac{1}{3}} - k) + c(k^{\frac{2}{3}} - k^{\frac{4}{3}}) = 0
  5. Coefficients analysis: Since kk is not a perfect cube, k1/3k^{1/3} is not an integer, and thus 11, k1/3k^{1/3}, k2/3k^{2/3}, and kk are all distinct.
  6. Final coefficients analysis: Therefore, the coefficients of 11, k1/3k^{1/3}, and k2/3k^{2/3} must all be zero for the equation to hold true:\newlinea(1k1/3)=0a(1 - k^{1/3}) = 0\newlineb(k1/3k)=0b(k^{1/3} - k) = 0\newlinec(k2/3k4/3)=0c(k^{2/3} - k^{4/3}) = 0
  7. Final coefficients analysis: Therefore, the coefficients of 11, k1/3k^{1/3}, and k2/3k^{2/3} must all be zero for the equation to hold true:\newlinea(1k1/3)=0a(1 - k^{1/3}) = 0\newlineb(k1/3k)=0b(k^{1/3} - k) = 0\newlinec(k2/3k4/3)=0c(k^{2/3} - k^{4/3}) = 0Since k1/3k^{1/3} is not 11, aa must be 00.\newlineSince k1/3k^{1/3} is not k1/3k^{1/3}11, k1/3k^{1/3}22 must be 00.\newlineSince k2/3k^{2/3} is not k1/3k^{1/3}55, k1/3k^{1/3}66 must be 00.

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