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# Finding an error in polynomial subtraction

CCSS.Math:

## Video transcript

Kaneesha is asked to subtract 7 b squared minus 5b plus 1 from 2 b squared plus 3b plus 11 her work is shown below and we see all the steps that she took and then they said which step did Kenisha make an error and it's pretty clear she made an error because they're not giving us an option that she didn't make an error so let's see what went on here so the first thing is we want to subtract 7 B squared minus 5b plus 1 we want to subtract that from 2 B squared plus 3b plus 11 and we see then step one she set it up properly she is indeed subtracting she is indeed subtracting 7 B squared minus 5b plus 1 from 2 B squared plus 3b plus 11 that's fair all right so step one seems to be okay now let's see step two it looks like she's going to distribute the negative sign so neg the negative of 7 B squared is I usually say this negative 7 B squared we're gonna subtract 7 B squared and then you have the negative of negative 5 B well that's going to be positive 5 B so this right over here this one over here should this over here should be a positive 5 B let me do that in a new color so this should be a positive 5 B and then the negative of positive 1 this should be a negative 1 that should be a negative 1 right over there so she's making a mistake she's making a mistake in step two when she distributes this negative sign so step two is where she made is where she actually made her error from there it seems reasonable she is subtracting the coefficients on the B squared terms so 2 B squared minus 7 B squared it gets us this right over there then on the B terms you have 3 B and then let's see you have it should be 3 B plus 5 B if she distributed the negative sign right but since she didn't distribute the negative sign right she has 3 B minus 5b and it should be 11 minus 1 but since she didn't do the distribution correctly we have 11 she has it should be 11 minus 1 as we said before because you're gonna just to be this negative sign but she left that as a plus one and so that's why she got that over there so her a real mistake was clearly in step two because from there on she's doing reasonable things it's just you mean that that one error