Oh Wise Ones,

I have a chart that gave me the equation
below. When I tried to solve for x, I keep getting
unexpected results. What am I doing wrong?

B5=1.1563 inches, B8=.76lbs
D5=.6875 inches, D8=.34lbs
When I solve for y (courtesy algebrahelp.com) I don't get
the correct results. From the cell relationships above if
C5 contains 1.1250 inches, it should yield a lbs result
between .76 and .34. I get: x = 1.066552901

Trend gives me: y = -0.4688x + 1.625


Mike

Simplifying
1.125 = -0.4688x + 1.625

Reorder the terms:
1.125 = 1.625 + -0.4688x

Solving
1.125 = 1.625 + -0.4688x

Solving for variable 'x'.

1.125 + 0.4688x = 1.625 + -0.4688x + 0.4688x

1.125 + 0.4688x = 1.625 + 0.0000
1.125 + 0.4688x = 1.625

1.125 + -1.125 + 0.4688x = 1.625 + -1.125

0.000 + 0.4688x = 1.625 + -1.125
0.4688x = 1.625 + -1.125

1.625 + -1.125 = 0.5
0.4688x = 0.5

x = 1.066552901

Mike -

Two points:

1. Make sure you're getting lots of significant digits in the equation.
Double click the label containing the equation, and on the Number tab,
choose a scientific or number with lots of decimal digits.

2. Make sure you've created an XY Scatter chart, not a Line chart. The
line chart uses 1, 2, 3 for its X calculations, while the scatter chart
uses the actual numerical X values.

- Jon
-------
Jon Peltier, Microsoft Excel MVP
Peltier Technical Services
Tutorials and Custom Solutions
http://PeltierTech.com/
_______

Mike K wrote:

Oh Wise Ones,

I have a chart that gave me the equation
below. When I tried to solve for x, I keep getting
unexpected results. What am I doing wrong?

B5=1.1563 inches, B8=.76lbs
D5=.6875 inches, D8=.34lbs
When I solve for y (courtesy algebrahelp.com) I don't get
the correct results. From the cell relationships above if
C5 contains 1.1250 inches, it should yield a lbs result
between .76 and .34. I get: x = 1.066552901

Trend gives me: y = -0.4688x + 1.625


Mike

Simplifying
1.125 = -0.4688x + 1.625

Reorder the terms:
1.125 = 1.625 + -0.4688x

Solving
1.125 = 1.625 + -0.4688x

Solving for variable 'x'.

1.125 + 0.4688x = 1.625 + -0.4688x + 0.4688x

1.125 + 0.4688x = 1.625 + 0.0000
1.125 + 0.4688x = 1.625

1.125 + -1.125 + 0.4688x = 1.625 + -1.125

0.000 + 0.4688x = 1.625 + -1.125
0.4688x = 1.625 + -1.125

1.625 + -1.125 = 0.5
0.4688x = 0.5

x = 1.066552901

In addition to Jon's suggestions, consider using the LINEST function to
get the regression coefficients directly in worksheet cells.

--
Regards,

Tushar Mehta
www.tushar-mehta.com
Excel, PowerPoint, and VBA add-ins, tutorials
Custom MS Office productivity solutions

In article ,
says...
Oh Wise Ones,

I have a chart that gave me the equation
below. When I tried to solve for x, I keep getting
unexpected results. What am I doing wrong?

B5=1.1563 inches, B8=.76lbs
D5=.6875 inches, D8=.34lbs
When I solve for y (courtesy algebrahelp.com) I don't get
the correct results. From the cell relationships above if
C5 contains 1.1250 inches, it should yield a lbs result
between .76 and .34. I get: x = 1.066552901

Trend gives me: y = -0.4688x + 1.625


Mike

Simplifying
1.125 = -0.4688x + 1.625

Reorder the terms:
1.125 = 1.625 + -0.4688x

Solving
1.125 = 1.625 + -0.4688x

Solving for variable 'x'.

1.125 + 0.4688x = 1.625 + -0.4688x + 0.4688x

1.125 + 0.4688x = 1.625 + 0.0000
1.125 + 0.4688x = 1.625

1.125 + -1.125 + 0.4688x = 1.625 + -1.125

0.000 + 0.4688x = 1.625 + -1.125
0.4688x = 1.625 + -1.125

1.625 + -1.125 = 0.5
0.4688x = 0.5

x = 1.066552901