What do opposite rays form

they form a single straight line:)

a line

Step-by-step explanation:

Here is ray AB  

     A                         B

     ++>

It starts at point A, goes through point B, and goes only in one direction, to the right. Points A and B lie on line AB.

Now I'll add an opposite ray whose endpoint is also point A.

             C                A                         B

<+++>

Ray AC also lies on the same line as ray AB, but starting at point A, it goes in the opposite direction of ray AB. When you add ray AC to its opposite ray AB, you get the entire line AB.

a line

d) -1

step-by-step explanation:

because linear equations are a lot simpler than quadratics equations, and linear equations formula is a lot easier to memorize. that's why i think they're harder.