Question 939469
a + b(x^3 + 3x^2 + 3x+1) + c(8x^3 + 12x^2 + 6x + 1) + d(27x^3 + 27x^2 + 9x + 1) = x^3
...
3b + 12c+ + 27d = 0 ( x^2 terms)
3b + 6c + 9d = 0 (x terms)
b + 8c + 27d = 1  (x^3 terms)
b = 1/2,    c = -1/2,    d = 1/6
....
a + b + c + d = 0 (constant terms) a = -1/6
*[invoke cramers_rule_3x3 3,12,27,0,3,6,9,0,1,8,27,1]