Verify that the indicated complex number is a zero of the given polynomial function. Find all other zeros and then give complete factorization. 2i: f(x)=3x^3-5x^2+12x-20

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?

If f(x)= 3x+6 which of the following is the inverse of f(x)

What is x and y intercepts for y=x+7