# Function Range.

• Jul 28th 2009, 04:55 PM
el123
Function Range.
Ok so i have this problem , i know this topic has been written about before cos i have read all the info i could find!! But im still stumped on this one.

The question is y= (x+1)(X-2)

The answer says domain is all real numbers and rane is all real numers greater than -2.25

Im lost as to how that -2.25 came up.
• Jul 28th 2009, 05:14 PM
skeeter
Quote:

Originally Posted by el123
Ok so i have this problem , i know this topic has been written about before cos i have read all the info i could find!! But im still stumped on this one.

The question is y= (x+1)(X-2)

The answer says domain is all real numbers and rane is all real numers greater than -2.25

Im lost as to how that -2.25 came up.

the function is quadratic, hence the graph of y is a parabola that opens upward in this case. the y-value of the vertex of the parabola is the least value in the range.

y = (x + 1)(x - 2)

the vertex is located at x = 0.5, midway between the two roots of the function.

the y-value of the vertex is y = (0.5 + 1)(0.5 - 2) = (1.5)(-1.5) = -2.25
• Jul 28th 2009, 07:26 PM
el123
Huzzahh!! Thank you Skeeter.