# How do I find the two variables a and n?

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In the expansion of #(1+ax)^n# the first three terms are 1+(5/3)x + (10/9) #x^2# what is a and what is n?

In the expansion of

##### 1 Answer

Jun 18, 2018

#### Explanation:

To solve this you need to know the formula for the binomial expansion of

In our situation we only need the first 3 terms:

=

Therefore

or

For this to work properly we notice that a=1/3, since n must be a natural number, therefore n=5

Test:

Our expression, then, is