Expand (a+b)3 in descending powers of a

Explanation:

The coefficients of each term, from left to right are 1, 3, 3, 1

These coefficient values are found in Pascal's triangle in the third row.

The variable terms will have variable terms in the form a^m*b^n. To start off, m = 3 and n = 0 to get a^3*b^0 = a^3*1 = a^3. From there you will have m count down (3,2,1,0) and n will count up (0,1,2,3)

So for the second term we have m = 2 and n = 1 to get the variable term a^2*b^1 = a^2b

The third term has m = 1 and n = 2 to get the variable term a^1*b^2 = ab^2

Finally the last term has m = 0 and n = 3 to get a^0*b^3 = 1*b^3 = b^3

Those variable terms are them multiplied with the coefficients mentioned previously to get the final answer.

Another way you can do this problem is to use the distributive property and FOIL rule

(a+b)^3 = (a+b)(a+b)^2

(a+b)^3 = (a+b)(a^2+2ab+b^2) FOIL rule

(a+b)^3 = a(a^2+2ab+b^2) + b(a^2+2ab+b^2) ... distribute

(a+b)^3 = a*a^2+a*2ab+a*b^2 + b*a^2+b*2ab+b*b^2 ... distribute again

(a+b)^3 = a^3 + 2a^2b + ab^2 + a^2b + 2ab^2 + b^3

(a+b)^3 = a^3 + 3a^2b + 3ab^2 + b^3

i would say c is the best answer, hope it's right!

good luck! =)

cutie~