Question 450956: Why Can The Variable X Be Substituded For Two Numbers?
Answer by ilana(307)   (Show Source):
You can put this solution on YOUR website! It looks like you are trying to figure out why 2 numbers can both be substituted in for x in a quadratic equation. The reason is a quadratic equation has 2 values of x that make it true. An equation can have even more than 2 solutions- the equation x + 3 = x + 5 - 2 is true for any value of x.
You can think of it graphically, too. The graph of a linear equation is a line. When you solve the equation x + 5 = 10, you get the solution x = 5. That means that when you graph the equation y = x + 5, the value of y is 10 when x = 5.
The graph of a quadratic equation is a parabola- it looks like a U. So sometimes more than one x-value will give the same y-value. x^2 - 2 = 14 when x is 4 and -4. When you look at the graph of y = x^2 - 2, the value of y is 14 when x is 4 and -4.
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