Question

Help! What does the bracket mean and how do I do the questions?

Answer 1

Answer:

The bracket is the binomial.

The definition is: $\binom{n}{k} = \frac{n!}{k!\cdot (n-k)!}$

Note that $\binom{n}{k} = \binom{n}{n-k}$

The meaning is "if we have n elements, how many ways are there to choose k of them?" From this definition it should be obvious that $\binom{n}{k} = \binom{n}{n-k}$ - if you're picking k, it's just as many ways as choosing the (n-k) that you're not picking.

The coefficient can be found by realizing that to get x^9, we need to choose (from the full multiplication):

• 9 brackets to provide x
• 2 brackets to provide the number 3

There's $\binom{11}{9}$ ways to do that, so the component for x^9 will be:

$\binom{11}{9} \cdot 3^2 \cdot x^9 = \frac{11!}{2!\cdot 9!} \cdot 3^2 \cdot x^9 = \frac{10\cdot 11}{2} \cdot 3^2 \cdot x^9 = 55 \cdot 9 \cdot x^9 = 495x^9$

So:

a = 2

Coefficient is 495

Answer 2

Answer:

maybe it meane 11/a

Step-by-step explanation: