Let, coordinate of centroid is (h,k) and coordinate of point P is (α,β)
We know that the centroid of a triangle with vertices (x1,y1),(x2,y2) and (x3,y3) is (3x1+x2+x3,3y1+y2+y3).
Hence, in ΔPQR, we have 3α+1+3=h and 3β+4−2=k
⇒α=3h−4, β=3k−2
Since (α,β) lies on the line 2x−3y+4=0
Hence, 2(3h−4)−3(3k−2)+4=0
⇒6h−9k+2=0
For finding the locus replace (h,k) by (x,y)
Hence, the locus of centroid is 6x−9y+2=0 which has slope =−(−9)6=32 since the slope of a line ax+by+c=0 is −ba.