00:01
Right, so for the question that we're asked today, we need to find the third term of expansion for the following expression.
00:06
And that expression is a minus b to the power of 30.
00:14
So we know that anything that is a plus b to the power of n is equal to the sum of n.
00:32
N, k starting at zero, n choose k, a to the power of n minus k, and then b to the power of k.
00:50
But in this case, we would have to use a negative b because the b we have in our question is minus b.
00:59
So what ours would look like, so therefore a minus b to the the power of 30 would look something like this.
01:10
30 on the top, k is equal to 0, and we have 30 choose k, a to the power of 30 minus k, and then b to the power of k, sorry, negative b to the power of k.
01:31
So for, let's use that symbol to represent the third term, so that means third term, we know that k is equal to that minus 1.
02:05
So therefore, k is equal to 2.
02:10
So now we know that k is equal to 2, we can find the coefficient for it...