Question 1194665
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You can use the Binomial Theorem to expand out (a+b)^3
More detail about that can be found here
<a href = "https://www.mathsisfun.com/algebra/binomial-theorem.html">https://www.mathsisfun.com/algebra/binomial-theorem.html</a>
You should find that 
(a+b)^3 = a^3+3a^2b+3ab^2+b^3



Here's another approach:
(a+b)^2 = a^2+2ab+b^2 by the FOIL rule
(a+b)^3 = (a+b)(a+b)^2
(a+b)^3 = (a+b)(a^2+2ab+b^2)
(a+b)^3 = c(a^2+2ab+b^2)
(a+b)^3 = c(a^2)+c(2ab)+c(b^2)
(a+b)^3 = a^2(c) + 2ab(c) + b^2(c)
(a+b)^3 = a^2(a+b) + 2ab(a+b) + b^2(a+b)
(a+b)^3 = a^2(a)+a^2(b)+2ab(a)+2ab(b)+b^2(a)+b^2(b)
(a+b)^3 = a^3+a^2b+2a^2b+2ab^2+ab^2+b^3
(a+b)^3 = a^3+3a^2b+3ab^2+b^3


I let c = a+b so we could use the distribution rule.


Take notice that the coefficients are 1, 3, 3, 1 which are found in Pascal's Triangle.


You can use the box method as a way to visually organize the terms
More info found here: 
<a href = "https://www.algebra.com/tutors/box-method.lesson">https://www.algebra.com/tutors/box-method.lesson</a>
<a href = "https://www.onlinemath4all.com/multiplying-polynomials-box-method.html">https://www.onlinemath4all.com/multiplying-polynomials-box-method.html</a>

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