# Check an expression in a Table Correct

I am working on a self-checking table and I’m able to get the table to check correctly for the first two expressions by using the following code:

a1=table9.cellContent(1,2)
check1=simpleFunction(a1,“x”).evaluateAt(2)=20 and countNumberUsage(a1,6)=1
cellContent(1,3):
when check1 “ ” otherwise “ However, it’s not correctly checking the last expression in the table:

a3=table9.cellContent(3,1)

check3=simpleFunction(a3,“x”).evaluateAt(2)=0 and countNumberUsage(a3,-2)=1

cellContent(3,3):
when check3 “ ” otherwise “ I think there is a problem with the countNumberUsage and the negative number. Any suggestions? Here’s a link to the example I’m working on… Table Self Check Example • Activity Builder by Desmos

Yes, countNumberUsage doesn’t take negatives, just make it 2.

Careful, just checking those two things makes it really easy to break:

source:

Original activity updated with countNumberUsage for 2.

That’s originally why I was trying to search for the negative 2. However, I think if I just search for the 3, in (x-2)(x-3) it will have the same effect and avoid the issue of counting the squared . I also added in another value check to avoid accepting (x-2)(x+3). Do you think that’s strong enough to check corectly?

I had to try a little harder but I could break it:

If you want to be completely certain, check three points each to make sure its a curve and count both the number total and the individual totals for each number in the expression.

countNumberUsage can count how many numbers are used in a latex string. Say a student enters `3x^2+14x-2`.
`countNumberUsage(inputName.latex)` would output 4, counting the 3, 2 2’s, and 14. Note: It counts numbers, not digits.
`countNumberUsage(inputName.latex, 14)` would output 1. You cannot enter negative numbers for the second parameter.