Saved Bookmarks
| 1. |
If `|a|=|b|=1 and |a+b|=sqrt(3)`, then the value of `(3a-4b)(2b+5b)` isA. `-21`B. `-(21)/(2)`C. `21`D. `(21)/(2)` |
|
Answer» Correct Answer - B Given ,`|a|=|b|=1 and |a+b|=sqrt(3)` `rArr |a|^2+|b|^2+2a.b=3` `a.b=(1)/(2)[because|a|^2=1|b|^2=1]` `therefore(3a-4b).(2a+5b)=6|a|^2+15a.b-8a.b-20|b|^2` `=6+7a.b-20=-(21)/(2)[becausea.b=(1)/(2)]` |
|