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Algebra Difficulty 4.8 AIME Prove it Ireland

Find all pairs (t,x)(t, x) of real numbers that satisfy
t33t2+3tx=0and t^3 - 3t^2 + 3t - x = 0 \quad \text{and}
27(x1)4+(1x2)3=0. 27(x-1)^4 + (1-x^2)^3 = 0.

Solution

With s=t1s = t - 1 we have s3=t33t2+3t1s^3 = t^3 - 3t^2 + 3t - 1, and the first equation can be written as x=s3+1x = s^3 + 1. From the second equation we get 27(s3)4=(x21)327(s^3)^4 = (x^2 - 1)^3, hence, by taking cube roots, 3s4=x213s^4 = x^2 - 1, i.e. x2=3s4+1x^2 = 3s^4 + 1. Comparing with the square of x=s3+1x = s^3 + 1 we obtain
3s4+1=s6+2s3+1, or 3s^4 + 1 = s^6 + 2s^3 + 1, \text{ or}
s63s4+2s3=0,i.e. s^6 - 3s^4 + 2s^3 = 0, \text{i.e.}
s3(s1)2(s+2)=0. s^3(s - 1)^2(s + 2) = 0.
So, s=2,0,1s = -2, 0, 1, i.e., t=s+1=1,1,2t = s + 1 = -1, 1, 2 and x=s3+1=7,1,2x = s^3 + 1 = -7, 1, 2. The three solutions (t,x)(t, x) are (1,7)(-1, -7), (1,1)(1, 1) and (2,2)(2, 2).

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