If the average variable cost curve is above the marginal cost curve, then Group of answer choices A. average variable costs must be increasing. B. marginal costs must be increasing. C. marginal costs must be decreasing. D. marginal costs can be either increasing or decreasing.

Here is their argument. given the obtuse angle x, we make a quadrilateral abcd with ∠dab = x, and ∠abc = 90◦, and ad = bc. say the perpendicular bisector to dc meets the perpendicular bisector to ab at p. then pa = pb and pc = pd. so the triangles pad and pbc have equal sides and are congruent. thus ∠pad = ∠pbc. but pab is isosceles, hence ∠pab = ∠pba. subtracting, gives x = ∠pad−∠pab = ∠pbc −∠pba = 90◦. this is a preposterous conclusion – just where is the mistake in the "proof" and why does the argument break down there?

How do you use the elimination method for this question? explain, because i really want to understand!

F(n + 1) = f(n) – 8. if f(1) = 100, what is f(6)?