Final answer:
If two planes intersect, they intersect in exactly one line.
Step-by-step explanation:
Premise 1: Planes R and S intersect.
Premise 2: Two planes can only intersect in two ways: either they intersect in exactly one line or they intersect in infinitely many lines.
Conclusion: Planes R and S intersect in exactly one line.
Step-by-step explanation:
Premise 1 states that Planes R and S intersect. Premise 2 states that there are only two possible ways for two planes to intersect. Since Premise 1 eliminates one of those possibilities (that Planes R and S intersect in infinitely many lines), the only remaining possibility is that Planes R and S intersect in exactly one line.
Therefore, we can conclude that Planes R and S intersect in exactly one line.