6 replies to this topic

[Serj]

I did a solve(0.5 * 1E-4 * 32 * (x-0.7)^2 -4E-4 = 0, x) and it gave me these solutions:
x=0.9 or x=1.9 . Which are completely wrong and really screwed me because this was during an exame, I only have this calc over a month and it's really pissing me off . Any comments?

Oh and I have os 3.1 ..

[Serj]

I discovered something new, if i do the solve( in Standard it gives me a solution that is 6/5, which is 1.2 and is the right solution.

Is this a bug, if so its really stupid, like the not being able to do comples exponentials in degrees. Very bad Casio

[vanhoa]

I found nothing wrong...

(CPM OS 3.0)

[Serj]

Thanks for the reply.

Doing it that way also gives me the right answer.. but doing exactly solve(0.5 * 1E-4 * 32 * (x-0.7)^2 -4E-4 = 0, x)
it still gives the error. Vanhoa, it this normal?

[vanhoa]

Yes... This is not normal.

0.9 and 1.9 are roots of (x-7/5)^2/625-1/2500
but your equation is (x-7/10)^2/625-1/2500

I dont know why 7/10 can be changed to 7/5 ...

[vanhoa]

Let's take a look:

(CPM OS 3.0)
This is calculated in both decimal and standard mode:

solve( a * ( x - b ) ^ 2 = c )
{x=b-(a*c)^0.5/a,x=b+(a*c)^0.5/a}


And then:
This is calculated in standard mode:

solve( a * ( x - b ) ^ 2 = c | b = 0.1 )
{x=(-(a*c)^0.5)/a+0.1,x=(a*c)^0.5/a+0.1}

This is calculated in decimal mode:

solve( a * ( x - b ) ^ 2 = c | b = 0.1 )
{x=(-(a*c)^0.5)/a+0.2,x=(a*c)^0.5/a+0.2}

But:
This is calculated in standard mode:

solve( a * ( x - b ) ^ 2 = c | b = 1 )
{x=(-(a*c)^0.5)/a+1,x=(a*c)^0.5/a+1}

This is calculated in decimal mode:

solve( a * ( x - b ) ^ 2 = c | b = 1 )
{x=(-(a*c)^0.5)/a+1,x=(a*c)^0.5/a+1}


=> if b is decimal, it is multiplied by 2


(Only on OS 3!)

[Serj]

Damn Vanhoa.. you really must have a programmers brain because you decomposed that to see where the algorithm was wrong. It is the most straight forward one, but maybe it makes an error while rewriting that equation. Anyway one more for the bug list.