Hello there. To solve this question, we'll need to remember how to calculate the binomial expansion of a expression.
Given an expansion on the expression (a + b)^n, we'll have something like:
a^n + k_1 . a^(n-1) b + k_2 . a^(n - 2) . b^2 + ....
These k_i numbers are the Pascal triangle coefficients, also binomial coefficients, that can be found using factorials.
But, without the need to finding those coefficients everytime, we already know a formula for the binomial expansion with power 2
(a + b)² = a² + 2ab + b²
Now, we rewrite it that way:
(y - 6)² = (y)² + 2(y)(-6) + (-6)²
Remember that (-a)^n = a, if n is even
= -a, if n is odd
Thus, we have:
y² - 12y + 36.
Another way of solving it is:
Make the square a product of two equal factors:
(y - 6)² = (y - 6)(y - 6)
Now, apply the FOIL
y² - 6y - 6y + 36
y² - 12y + 36