If a △ABC have vertices A(−1,7),B(−7,1) and C(5,−5), then its orthocenter has coordinates:
(A)(53,−53)
(B)(−3,3)✓ Correct
(C)(3,−3)
(D)(−53,53)
Answer: (B)
Solution
The orthocentre is where two altitudes meet. Side BC has slope 5+7−5−1=−21, so the altitude from A, perpendicular to it, has slope 2: y−7=2(x+1), that is y=2x+9. Side AC has slope 5+1−5−7=−2, so the altitude from B has slope 21: y−1=21(x+7), that is y=2x+29. Solving the two, 2x+9=2x+29 gives x=−3 and then y=3. The orthocentre is (−3,3).
JEE Main · 2020 · 03 Sep 2020 · Shift 2 · Single correct option