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Showing posts with label cell reference. Show all posts
Showing posts with label cell reference. Show all posts

Sunday, February 22, 2015

How to draw a circle in Excel

Microsoft Excel has various graphing options. The x-y chart allows us to draw any points or lines and it will automatically connects those points  to form a curve. We can use x-y chart to create a circle which can change its radius and center point.

To draw a circle in excel, first we have to prepare a table for x and y from angle (f) = 0 to f =360 deg. However, we have to modify the formula since Microsoft Excel uses radian instead of degree to calculate value of sine and cosine.

To convert angle from degree to radian, we use

Angle (rad) = Angle (deg.) x pi/180

Value of pi in excel can be referred as PI()
Therefore the formula of x and y become...

x= rcos(fxPI()/180)
y= rsin(fxPI()/180)

To offset the center point, the final formula becomes

x= rcos(fxPI()/180)+xc
y= rsin(fxPI()/180)+yc

In excel, after we write a formula in one cell, when dragging to other cells, it will change the cell reference. We can avoid this if we would like to let excel point to only desired cell by changing the reference with $ symbol by just repeatedly pressing F4.

Example:
Formula of x: write  =$D$3*COS($B8*PI()/180)+$D$4 instead of writing =D3*COS(B8*PI()/180)+D4

Using $D$3 will always refer to cell D3 which is the value of a radius.
If we write D3, after dragging the formula to other cells, the value of a radius will change to cell D4, D5, D6, ... which is wrong.