Equations of Perpendicular Lines

Directions: Using the digits 1 to 9 at most one time each, fill in the blanks to create two distinct perpendicular lines.  Note that the coefficient for the second line’s y is negative.

__ x + __ y = __

__ x + -__ y = __



What do the equations of perpendicular lines have in common?



There are many answers but the coefficients of x and y for each line must produce a product of -1.  For example, 2x + 3y = 5 and 6x + -4y = 7

Source: Bryan Anderson

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One comment

  1. If students know anything about equations of perpendicular lines then they must know about gradients or slopes of lines and also that the product of the slopes is -1. If they don’t then then are going to be using some other rule which doesn’t say anything else that is useful.

    I don’t understand the first line of the answer.

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