Powers of a + b
Each number in a row can be found by adding the 2 coefficients above it.
1
. . . but it’s easy to know which row we want as, for example,
Powers of a + b
The full expansion is
1
We know that
We know that
Powers of a + b
Solution:
The coefficients are
To get we need to replace a by 1
We know that
Powers of a + b
Solution:
The coefficients are
To get we need to replace a by 1 and
b by (- x)
1
(1)
1
(1)
(1)
(-x)
(-x)
(-x)
(-x)
(-x)
Simplifying gives
e.g. 2 Write out the expansion of in ascending powers of x.
We know that
Powers of a + b
Solution:
The coefficients are
Simplifying gives
e.g. 2 Write out the expansion of in ascending powers of x.
We know that
Powers of a + b
Solution:
The coefficients are
Simplifying gives
e.g. 2 Write out the expansion of in ascending powers of x.
We know that
Powers of a + b
Solution:
The coefficients are
Simplifying gives
We could go straight to
Powers of a + b
Solution:
The coefficients are
We will now develop a method of getting the coefficients without needing the triangle.
We know from Pascal’s triangle that the coefficients are
Powers of a + b
There is a pattern here:
So if we want the 4th coefficient without finding the others, we would need
( 3 fractions )
We can write
. . . gives the number of ways that 8 items can be chosen from 20.
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