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    				| 1. | If two vertices of a triangle are `(-2,3)`and `(5,-1)`the orthocentre lies at the origin, and the centroid on the line `x+y=7`, then the third vertex lies at`(7,4)`(b) `8,14)``(12 ,21)`(d) none of theseA. (7,4)B. (8,14)C. (12,21)D. none of these | 
| Answer» Correct Answer - D Given O(0,0) is the orhtocenter . Let A(h,k) be the third vertex, and `B(-2,3)` and `C(5,-1)` the other two vertices. Then the slope of the line through A and O is k/h. while the line through B and C has the slope `-4//7`. By the property of the orthocenter, these two lines must be perpendiuclar. So, we have `(k/(h))(-(4)/7)=-1or (k)/(h)=(7)/(4)`....(1) Also, ` (5-2+h)/(3)+(-1+3+k)/(3)=7` ....(ii) `h+k=16` | |