FAQ: Introduction to Linear Algebra - Inverse Matrices

This community-built FAQ covers the “Inverse Matrices” exercise from the lesson “Introduction to Linear Algebra”.

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This exercise can be found in the following Codecademy content:

Fundamental Math for Data Science

FAQs on the exercise Inverse Matrices

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I’m probably missing something but I feel like the instructions on the left don’t match the animation on the right. I just got confused. Please explain it to me.

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I think I’m seeing the same thing @ethan.dutton327 was seeing. In step 4 you have us multiplying 3/2 by the values in row 2 and adding it to the values in row 3. This doesn’t seem to break down to 0 as you’ve suggested. @codecademy I may be wrong, but I’d like to at least understand if I’m missing somthing.

Thanks!

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Hi @ptrdmr

Are you talking about the computation from Slide 2 to 3?

It looks like we start with the following in Rows 2 and 3 on Slide 2:

R2: 0,-3,-2 | 0,1,-1
R3: 0,2,1 | 1,0,0

On Slide 3, the calculation is (3/2)*R3 + R2

Let’s look at what happens with the first two entries of R3 in this calculation:

col 1: (3/2)*0 + 0 = 0
col 2: (3/2)*2 + (-3) = 3 + (-3) = 0

I think you may have tried multiplying 3/2 by the value in row 2, not row 3?

Let me know if that clears it up (or if I’ve misunderstood the sticking point…)

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Ahh! I think the phrasing was a little dicey, and I swapped the rows in the equation. I’m all straight now. Thank you for clarifying!

Just here to agree with the above comments. the animations is correct, but the instructions (so far, i just noticed it on step 4) kind of words it like we are supposed to add 3/2 of row 3 to the values of row 2 (even though at the beginning of that sentence, it says to cancel out the first two entries of row 3) very confusing instructions :frowning:

i believe it should instead say:
‘cancel out the first two entries of row 3 by adding each value of row 2 to 3/2 of each value of row 3’