Expand (4x-3y) ^4 using pascal's triangle ... ?

Using row 4:

coefficients are: 1, 4, 6, 4, 1

a^4 + a^3b + a^2b^2 + ab^3 + b^4

Now adding the coefficients:

1a^4 + 4a^3b + 6a^2b^2 + 4ab^3 + 1b^4

Substitute a and b:

a = 4x

b = - 3y

1 (4x) ^4 + 4 (4x) ^3 (-3y) + 6 (4x) ^2 (-3y) ^2 + 4 (4x) (-3y) ^3 + 1 (-3y) ^4

Now simplify the above:

256x^4 - 768x^3y + 864x^2y^2 - 432xy^3 + 81y^4