Stage: 4 Challenge Level: 
Four straight lines have the
following equations:
How many intersections do you expect ?
Three of these four lines enclose a triangle which has only negative co-ordinates for any point on that triangle.
Which three lines ?
Simultaneous equations. Short problems. Solving equations graphically. Forces. Positive-negative numbers. Working systematically. Rigid Bodies. engineering. physics. Manipulating algebraic expressions/formulae.
Published January 2008.
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