Ptolemy a) Prove the sum formula, 120 crd(180º – (a + b)) = crd(180° – a) crd(180° – B) – crd(a) crd(B), using Ptolemy's formula on quadrilaterals inscribed in a circle. b) Use Ptolemy's difference formula to calculate crd(12°) and then apply the half-angle formula to calculate crd(6°) and crd(30). Note: Use decimal numerical system for your calculations. You may use that crd(72°) = 70; 32, 3. Compare your result to Ptolemy's: crd(3°) = 3; 8, 28 and crd(69) = 6; 16; 49.

answer: c.  

step-by-step explanation:

mixtures containing substances that get attracted to magnet can be separated using a magnet. we can separate iron from a mixture of sand and iron, as only iron attracts to the magnet.

let's call the solutions x₁ = (5 - 2√7)/3 and x₂ = (5 + 2√7)/3

then the equation is (x-x₁)(x-x₂) = 0

if you fill that in you get a lot of numbers which you can recognize as ax²+bx+c=0.

step-by-step explanation:

you can see that a=1 (there is just an x²)

b = (-5 -2√7 + 2√7 - 5)/3 = -10/3

c = -2√7)/3 ) * (-5+2√7)/3) = -1/3

so your answer is 3x^2 – 10x – 1 = 0