binomial expansion for positive integers

Question 1

what is the given binomial expansion formula?

Answer 1

(a + b)^n = a^n + nC1 * a^(n-1) * b + …
nCr * a^(n-1) * b^r + … b^n

Question 2

what is the formula for nCr?

Answer 2

= n! / r!(n-r)!

Question 3

how do you approximate using a binomial expansion?

Answer 3

set approximation value equal to polynomial inside brackets (ignore the power on both)
make x the subject
sub x value into expansion.