Write linear equation in functional natation

• Oct 12th 2012, 12:01 PM
ford2008
Write linear equation in functional natation
Hey guys,

could somebody please check if the following is right?

Task: Write the linear equation 4x -9y = -45 in functional notation, and determine the x-and y-intercepts. Show your work using functional notation.

My work:

4x -9y = -45 is
-9y = -4x -45 is
y = -4/-9 x +5 is

f(x) = -4/-9 x +5

The x-intercept is where y=0
0 = -4/-9 x +5
-5 = -4/-9 x
x = -11.25

The y-intercept is where x=0
f(0) = -4/-9 (0) +5
f(0) = 0 +5
f(0) = 5

Is my whole work right or is there any mistake? Thank you.
• Oct 12th 2012, 12:05 PM
Plato
Re: Write linear equation in functional natation
Quote:

Originally Posted by ford2008
Task: Write the linear equation 4x -9y = -45 in functional notation, and determine the x-and y-intercepts. Show your work using functional notation.

$f(x)=\frac{4}{9}x+5$.
• Oct 12th 2012, 02:23 PM
HallsofIvy
Re: Write linear equation in functional natation
Quote:

Originally Posted by ford2008
Hey guys,

could somebody please check if the following is right?

Task: Write the linear equation 4x -9y = -45 in functional notation, and determine the x-and y-intercepts. Show your work using functional notation.

My work:

4x -9y = -45 is
-9y = -4x -45 is
y = -4/-9 x +5 is

-4/-9= 4/9 but you seem to recognize that later so it is just awkwardly written, not an error.

Quote:

f(x) = -4/-9 x +5

The x-intercept is where y=0
0 = -4/-9 x +5
-5 = -4/-9 x
x = -11.25

The y-intercept is where x=0
f(0) = -4/-9 (0) +5
f(0) = 0 +5
f(0) = 5

Is my whole work right or is there any mistake? Thank you.
Yes, those are correct.

I realize you were told to "Write the linear equation 4x -9y = -45 in functional notation" but, frankly, it would have been simpler to use the original form.
With 4x -9y = -45, setting y to 0 gives 4x= -45 so that x= -45/4= -11.25 is the x-intercept. Setting x= 0, -9y= -45 so that y= 5 is the y intercept.