$$\frac{(0.87)^3 + (0.13)^3}{(0.87)^2 + (0.13)^2 - (0.87) \times (0.13)}$$ is equal to
using identity $$ a^3 + b^3 = (a + b)(a^2 - ab + b^2) $$
here a = 0.87
b = 0.13
$$\frac{(0.87)^3 + (0.13)^3}{(0.87)^2 + (0.13)^2 - (0.87) \times (0.13)} = \frac{(0.87 + 0.13)(0.87)^2 + (0.13)^2 - (0.87) \times (0.13)}{(0.87)^2 + (0.13)^2 - (0.87) \times (0.13)} = 0.87 + 0.13 =1 $$
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