What is "if xy = 1?

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The equation "xy = 1" means that two numbers, x and y, multiplied together equal 1. In this case, x could be the reciprocal of y, or y could be the reciprocal of x. For example, if x = 3, then y would have to equal 1/3 in order for their product to equal 1. Another example would be if x = 2/5, then y would have to equal 5/2 in order for their product to equal 1. This equation is often useful in algebraic manipulation and solving equations.