Answers

2016-06-18T13:26:38+08:00
R²+t²+n²-2rt-2nt+2rn

steps:

square the 1st term
square the 2nd term
square the 3rd term
1st term times 2nd term times 2
2nd term times 3rd term times 2
1st term times 3rd term times 2

:))
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