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### High School Mathematics - 29.21 Collinearity of Points

 If three points (x1, y1), (x2, y2), (x3, y3) lie on a straight line, the area of the triangle formed by them is zero. i.e1/2(x1y2-x2y1+x2y3-x3y2+x3y1-x1y3) = 0 Example: Show that the points (a,b+c),(b,c+a) and (c, a+b) are collinear. The area of the triangle formed by the three points is = 1/2[a(c+a)-b(b+c)+b(a+b)-c(c+a)+c(b+c)-a(a+b)] =0 Hence the points are collinear. Directions: Solve the following problems.
 Q 1: For what value of x will the points (x,-1), (2,1) and (4,5) lie on a line.153 Q 2: Show that the points (1,4), (3,-2) and (-3,16) are collinear.Answer: Q 3: Find the condition that the point (x,y) may lie on the line joining (3,4) and (-5,-6).5x+1 = 05x-4y+1 = 0x-4y = 0 Q 4: Show that (-5,1), (5,5) and (10,7) are collinear.Answer: Q 5: For what value of k do the points (-1,4), (-3,8) and (-k+1,3k) lie on a straight line.503 Q 6: If (7,a),(-5,2) and (3,6) are collinear, find a.12158 Q 7: Show that the points (a2,0), (0,b2 and (1,1) are collinear.Answer: Q 8: Prove that the points (4,2), (7,5) and (9,7) are collinear.Answer: Question 9: This question is available to subscribers only! Question 10: This question is available to subscribers only!