The slant height is 39. If you need work show, let me know.
By saying the slope was multiplied by -1/2, I assume you actually mean multiply and not decreased. In the equation, the slope of the equation is 3. Therefore, if it were to be multiplied by -1/2, the new slope would be -3/2. Because the slope is now negative, the slow would be downward. I hope this helps :-)
A postulate (or sometimes called as an axiom) is something assumed rather than proven. A theorem is something that is proven. To make a theorem, we first start with undefined terms. Such as line, point, and plane. Then next comes the postulates. Then the definitions. And in some theorems, a previously proven theorem is sometimes used in order to prove the new theorem.
X° = 180° - 160°
= 20°
x = 20