Coolmath Algebra
Determinants and Cramer's Rule Lesson 2 -
Determinants for 3x3's -
Method 1
(page 1 of 4)
---- This algebra lesson explains a quick and easy
way to find a 3x3 determinant. |
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This is a trick that ONLY works
for 3 x 3's.
You cannot use it for 4 x 4's
and higher... For these, the formal approach is a gnarly thing
that expands around a row or column and uses critters called
"minors." However, I highly recommend a computer or graphing
calculator. If you go on to take Calculus 3 or Linear Algebra,
you'll need the "real" 3 x 3
technique, but it will be specialized and really easy to pick up.
On to the trick...
It works a lot like the
2 x 2
method where you
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multiply down and add... |
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and multiply up and subtract. |
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