SOLUTION: I am not sure that I chose the correct topic for the question. It is algebriac, but I am not sure of its specific topic. Anyway, here is the question: (r+2t)^3+(r-7t)^3 The ans

Algebra ->  Functions -> SOLUTION: I am not sure that I chose the correct topic for the question. It is algebriac, but I am not sure of its specific topic. Anyway, here is the question: (r+2t)^3+(r-7t)^3 The ans      Log On


   

Question 367599: I am not sure that I chose the correct topic for the question. It is algebriac, but I am not sure of its specific topic. Anyway, here is the question:
(r+2t)^3+(r-7t)^3
The answer is (2r-5t)(r^2+5rt+67t^2)
I cannot figure out how they got the 67t^2!
Answer by mananth(16946) About Me  (Show Source):
You can put this solution on YOUR website!
(r+2t)^3+(r-7t)^3
we use the formula of sum of two cubes
a%5E3%2Bb%5E3=+%28a%2Bb%29%28a%5E2-ab%2Bb%5E2%29
..
%28r%2B2t%2Br-7t%29%28%28r%2B2t%29%5E2+-%28r%2B2t%29%28r-7t%29%2B%28r-7t%29%5E2%29
%282r-5t%29%28r%5E2%2B4tr%2B4t%5E2-%28r%5E2-5t-14t%5E2%29%2Br%5E2-14tr%2B49t%5E2%29
..
%282r-5t%29%28r%5E2%2B4tr%2B4t%5E2-r%5E2%2B5tr%2B14t%5E2%2Br%5E2-14tr%2B49t%5E2%29
..
%282t-5r%29%28r%5E2-5tr%2B67t%5E2%29
m.ananth@hotmail.ca