in discussion Programming & Design / TI-83/84/+/SE Programming » How do I find intercepts between two graphs?
If you know the coefficients, you could use a quadratic solver since you know the two equations are quadratic. Basically, you just think of it as Y1-Y2=0.
However, if you don't want to input coefficients and just use the Y= vars directly, then it gets a bit complicated. Still doable though! The first thing you need to do is evaluate Y2-Y1 at three points. For convenience, we'll do -1, 0, and 1. From these three points, we can construct the coefficients:
Evaluate the three points:
Y1(⁻1)-Y2(⁻1→A
Y1(0)-Y2(0→B
Y1(1)-Y2(1→CInterpolate to get the coefficients:
.5(C-A→D
2(Ans+A-B→A(The quadratic equation is AX²/2+DX+B)
Now we just do our standard quadratic solver, but we'll add some safety checks:
If A:Then
D²-2AB
If Ans<0
Ans+0i
√(Ans→B
Disp (D-B)/A,(D+B)/A
Else
If D=0:Then
If B=0:Then
Disp "INTERCEPTS EVERYWHERE
Else
Disp "INTERCEPTS NOWHERE
End
Else
Disp ⁻B/D
End
EndNOTE: This only works if Y1 and Y2 are quadratic (i.e., ax²+bx+c, but a and/or b are allowed to be 0)
There may be easier ways on the newer calcs, I'm not sure, but this should work either way :)
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