SOLUTION: Hello! I have a question concerning the following problem. I know your supposed to use the COS formula however I do not know how to approach that method. Could you show me step -by

Algebra ->  Parallelograms -> SOLUTION: Hello! I have a question concerning the following problem. I know your supposed to use the COS formula however I do not know how to approach that method. Could you show me step -by      Log On


   

Question 31180: Hello! I have a question concerning the following problem. I know your supposed to use the COS formula however I do not know how to approach that method. Could you show me step -by- step?
Find the area of a parallelogram whose sides are 6 inches and 8 inches and whose longer diagonal is 12 inches.
Thank you so much!
Answer by longjonsilver(2297) About Me  (Show Source):
You can put this solution on YOUR website!
Given ANY triangle ABC where

length a is opposite angle A
length b is opposite angle B
length c is opposite angle C

then knowing just 3 sides, we can find an angle using the cosine rule, which states that:

+a%5E2+=+b%5E2+%2B+c%5E2+-2bc%2AcosA+

so put the values in, re-arrange to find cosA and hence find the angle A.

Note: we could have the formula as
+b%5E2+=+a%5E2+%2B+c%5E2+-2ac%2AcosB+ or
+c%5E2+=+a%5E2+%2B+b%5E2+-2ab%2AcosC+

it is completely flexible.

jon.