There are 8 marbles in a bag, all of different colors. In how many orders can 4 marbles be chosen? In other words, what is the number of permutations of picking 4 marbles from the bag?
A
1680
B
70
С
40320

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?

You can find the constant of proportionality by finding the ratio of

Choose the linear inequality that describes the graph. the gray area represents the shaded region. a: y ≤ –4x – 2 b: y > –4x – 2 c: y ≥ –4x – 2 d: y < 4x – 2