Which of the following expressions is equivalent to 4(2k + 7) – 5k(6k-2) ? A 30k2 + 2k + 28
B. -30k2 – 2k + 28
C. 30k2 + 18k + 28
D. -30k2 + 18k + 28

(the 2s next to the 30s mean to the second power)

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?

Find the solution of this system of equation -7x+y=-20 9x-3y=36

Which of the expressions (on the photo document i inserted) together represent all solutions to the following equation? 8cos(12x)+4=-4 *the answer should be in degrees.* > i would like for someone to explain the process to find the solutions for this.