Question 367599
(r+2t)^3+(r-7t)^3
we use the formula of sum of two cubes
{{{a^3+b^3= (a+b)(a^2-ab+b^2)}}}
..
{{{(r+2t+r-7t)((r+2t)^2 -(r+2t)(r-7t)+(r-7t)^2)}}}
{{{(2r-5t)(r^2+4tr+4t^2-(r^2-5t-14t^2)+r^2-14tr+49t^2)}}}
..
{{{(2r-5t)(r^2+4tr+4t^2-r^2+5tr+14t^2+r^2-14tr+49t^2)}}}
..
{{{(2t-5r)(r^2-5tr+67t^2)}}}

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