# Finding equations w/ two given points:

1. Oct 12, 2006

### AznBoi

Ok there are two give points and I need to find the equation:

Points: (-3,0), (-.5,0)

My work:

y=(x+3)(x+.5)
y=x^2+.5x+3x+15

Completed the square:

-15= x^2+3.5x
-15=x^2+3.5x+3.0625
-11.9375=(x+1.75)^2
y= (x+1.75)^2+11.9375

What did I do wrong??

2. Oct 12, 2006

### courtrigrad

$$y = (x+3)(x+.5) = x^{2}+3.5x + 1.5$$

you multiplied 3 by 5, instead of 3 by 0.5

3. Oct 12, 2006

### AznBoi

ohhh lol thanks.

4. Oct 12, 2006

### HallsofIvy

Staff Emeritus
Why did you assume a quadratic function? Two points determine a straight line. The constant function y= 0 passes through (-3, 0), (-5, 0).
In fact there are an infinite number of functions whose graph pass through those two points.

5. Oct 12, 2006

### courtrigrad

Halls, he meant the zeros of the function. He is doing quadratic equations after all.

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