First slide
Cartesian plane
Question

Two vertices of a triangle are (4,-3) and (-2,5). If the orthocenter of the triangle is at (1,2), then the third vertex is

Moderate
Solution

Let the third vertex be (h,k) 

Now, the slope of AD is (k−2)/(h−1), the slope of BC is (5+3)/(−2−4)=−4/3,the slope of BE is (−3−2)/(4−1)=−5/3, and the slope of AC is (k−5)/(h+2). Since ADBC, we have 

k−2h−1×−43=−1

or 3h−5k+31=0_______(i)

Again, since BEAC,, we have 

−53×k−5h+2=−1

or 3h−5k+31=0______(ii)

On solving (i) and (ii), we get h=33, k=26. Hence, the third vertex is(33,26)

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