decide if abcd is self-intersecting – Discussion Forum

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Kriti

Asked: September 28, 2026In: Class 9 Maths

Consider three non-collinear points A, B, C and draw the lines AB, BC, CA. For every possible location of point D in the plane outside these lines, decide if ABCD is self-intersecting, non-convex or convex. (Hint: the three lines divide the plane into 7 regions.)

Placing D inside △ABC yields a non-convex quadrilateral. In the region opposite vertex B or across segment AC, ABCD is convex. In the remaining four outer regions, ABCD is self-intersecting. class 9 maths ganita manjari part 2 chapter 12 question answer