Just for future reference always put ^ for exponents. The answer is y-6 though.
(y-4)(y-6) create that trinomial. You can prove that by using the FOIL algorithm
1+sin²x=2-cos²x
Remenber: sin²x+cos²x=1 ⇒sin²x=1-cos²x
1+sin²x=1+(1-cos²x)=2-cos² x (this is true)
All angles are congruent to its corresponding part. While all segments are similar to its corresponding part
