X^2+7xy-18y^2 how do i solve this i'm factoring trinomials

If sec theta = 5/3 and the terminal point determined by theta is in quadrant 4, then

1- is the product of two rational numbers irrational or rational? first, make a hypothesis by multiplying two rational numbers. then, use variables such as x=a/b and y=c/d and the closure property of integers to prove your hypothesis. 2- what do you think the product of a nonzero rational number and an irrational number is? is it rational or irrational? make use of variables, the closure property of integers, and possibly a proof by contradiction to prove your hypothesis. 3- why do we have to specify that the rational number must be nonzero when we determine what the product of a nonzero rational number and an irrational number is? if the rational number were 0, would it give us the same result we found in part b?

The price of one share of a company’s stock declined $13.89 every day for 2.5 days what was the stocks total decline in price