Which expression gives the unit length of the line segment with the endpoints (-12, 8) and (2, 8) |-12| + |2|
|-12| - |2|
|8| + |8|
|8| - |8|

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?

Ihave trouble finding the nth term of a linear sequence

Which expression is equal to (f+g)(x)?