An ice hockey puck has a volume of 113 cm3.
it is made out of rubber with a density of 1.5 grams per cm3. work out the mass of the ice hockey puck.

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?

Which of the following is best modeled using a linear equation y=ax+b, where a is less than 0?

Astudent showed the steps below while solving the inequality |x-4|< 1 by graphing.