I don't know if I did it right?

To solve the system of equations below, pedro isolated the variable y in the first equation and then substituted it into the second equation. what was the resulting equation? { 5y=10x {x^2+y^2=36

If the value of cos330°is√3/2 then find cos 165°.

Parallelogram efgh is a rectangle. he = 6, and fe = 8. find ge: and find fj: