Suppose a triangle has two sides of length 32 and 35, and that the angle between these two sides is 120°. Which equation should you solve to find the
length of the third side of the triangle?
A. C2 = 322 + 352 – 2(32)(35)sin120°
B. sin32
sin35
b
120
C. C= 32 + 35 - 2(32)(35)cos120°
D. 2 = 322 + 352 - 2(32)(35)cos120°

D

Step-by-step explanation:

It is the law of cos

C^2= A^2+B^2-2*A*B*cosL where L is the angle between A and B

so C = 32^2 + 35^2 - 2(32)(35)cos120°

x^2 + 81

we can factor this using difference of square binomials.

rewrite the equation:

x^2 - (-81)

factor:

(a^2 - b^2) = (√a^2 + √b^2)(√a^2 - √b^2)

(x^2 - (-81) = (x + √-81)(x - √-81)

we can remove the - from under the radical by multiplying it by i.

(x^2 - (-81) = (x + i√81)(x - i√81)

(x^2 - (-81) = (x + 9i)(x - 9i)

we can check our answer by using foil:

x^2 - 9ix + 9ix - 81i^2

x^2 - 81^2

i^2 = -1

x^2 + 81