SOLUTION: In the triangle below, side BC is 12 units long and side AC is 15 units long. If angle < C is 60 degrees, then what is side AB-squared? A. 64 B. 81 C. 189 D. 369 E. 549

Algebra ->  Triangles -> SOLUTION: In the triangle below, side BC is 12 units long and side AC is 15 units long. If angle < C is 60 degrees, then what is side AB-squared? A. 64 B. 81 C. 189 D. 369 E. 549       Log On


   

Question 943816: In the triangle below, side BC is 12 units long and side AC is 15 units long. If angle < C is 60 degrees, then what is side AB-squared?
A. 64
B. 81
C. 189
D. 369
E. 549
I tried using the Rule of Cosines, but I'm not getting any of the answer choices.
I did: AB-squared = AC-squared + BC squared - 2(AC)(BC)cos60
(AB)^2 = (15)^2 + (12)^2 - 2(15)(12)cos60
For (AB)^2 = 711.8686
Answer by MathLover1(20849) About Me  (Show Source):
You can put this solution on YOUR website!

if BC=12 units long, side AC=15 units long, and angle < C+=60 degrees, then we have
pay attention to the question: what is side AB-squared?
%28AB%29%5E2+=+15%5E2+%2B+12%5E2+-+2%2815%29%2812%29cos%2860%29.....cos%2860%29=1%2F2

%28AB%29%5E2+=+225+%2B+144+-+360%2A%281%2F2%29

%28AB%29%5E2+=+369+-+180

%28AB%29%5E2+=+189 => this is AB-squared

so, your answer is: C. 189