# calculating x when y is > 0

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Gavin Seddon on 13 Feb 2019
Commented: Gavin Seddon on 14 Mar 2019
Hello
I have plotted a changing distance (d(x)) with time using cftool and calculated the function. Its derivative was calculated and this is v(x). when plotted with fplot the initial Y values are 0. I am calculating the x position at which this rises above the x axes (y>0). To do this i made v(x) equivalent to 1 (==1) and evluated x yet:
>>v(x)==1
ans =
(4119*x^2)/10000 - (1787*x)/5000 + 891/2500 ==1
>> eval x
x =
x
Will someone please help to calculate this? i can measure the x value directly. It is preferable to standardise this procedure.
GS.
##### 2 CommentsShowHide 1 older comment
madhan ravi on 14 Feb 2019

Walter Roberson on 14 Feb 2019
solve(v(x)==1,x)
Gavin Seddon on 14 Mar 2019
Hello,
mytable.NewThirdColumn = double( subs( v, x, MyTable.(2)));
was the command used and yes indeed it produced a third column.
The numbers revealed indicate the method I tried previously was indeterminate. Thank you
GS.