I can't figure out the value of a- please help!

(6y - 11)(6y + 11)

 

All you need to do is "FOIL" this expression. That means multiply the First two terms  of each factor together, multiply the Outer two terms of each factor together, multiply the Inner two terms of each factor together, and multiply the Last two terms of each factor together. Then add each of those products together.

You can also think of this by saying,"The first term times the third and fourth term plus the second term times the third and fourth term." All this is doing is getting you to multiply each thing by every other thing.

So for this problem that will be:

 

= (6y)(6y) + (11)(6y) + (-11)(6y) + (-11)(11)

 

= 36y² + 66y - 66y - 121

 

= 36y² - 121

 

Now you can see that a = 36.