If \[m-5n=2,\] then the value of\[({{m}^{3}}-125{{n}^{3}}-30\,\,mn)\]is [SSC (CGL) 2015] |
A) 6
B) 7
C) 8
D) 9
Correct Answer: C
Solution :
Given, \[m-5n=2\] ... (i) |
On cubing both sides, we get |
\[{{(m-5n)}^{3}}={{(2)}^{3}}\] |
\[\Rightarrow \]\[{{m}^{3}}-125{{n}^{3}}-3\,\,(m)(5n)(m-5n)=8\] |
\[\Rightarrow \]\[{{m}^{3}}-125{{n}^{3}}-15mn\,\,(2)=8\] [from Eq, (i)] |
\[\Rightarrow \]\[{{m}^{3}}-125{{n}^{3}}-30mn=8\] |
You need to login to perform this action.
You will be redirected in
3 sec