Which of the following formulas shows the Law of Cosines? “Justify your answer”

Question

A) c^2 = a^2 + b^2 - 4ac + cosA

B) c^2 = a^2 - b^2 - -2abcosC

C) c^2 = a^2 + b^2 - 2cosC

D) (cos A)/a = (cosB)/b

Answer 1

B) is closest. it has an extra negative sign though

it might just be a typo

c^2 = a^2 +b^2 -2abCosC is the Law of Cosines

C is the angle opposite side c

a and b are the other two sides

a is opposite angle A

b is opposite angle C

the law of cosines is a general modified version of the Pythagorean Theorem when it's not a right triangle

if angle C =90 degrees, the Law of Cosines becomes the Pythagorean Theorem, with c as the hypotenuse and a and be the two other sides of a right triangle