All except combine like terms. Since you only have 1 variable.
Hope this helps.
r3t40
Option C:
The coefficient of
is 40.
Solution:
Given expression:

Using binomial theorem:

Here 
Substitute in the binomial formula, we get

Now to expand the summation, substitute i = 0, 1, 2, 3, 4 and 5.


Let us solve the term one by one.






Substitute these into the above expansion.

The coefficient of
is 40.
Option C is the correct answer.
For these kinds of expressions use FOIL (first, outside, inside, last).
-2x • 9x = -18x^2
-2x • -3y = 6xy
8y • 9x = 72 xy
8y • -3y = -24y^2
Now combine them all:
-18x^2 + 78xy - 24y^2
Answer:
We need dimensions to answer this.