00:01
Okay, so i have a parallelogram, right? quadrilateral opposite sides marks parallel.
00:07
And i'm told that the longer diagonal, so the longer diagonal of my parallelogram has a length of 45 .1.
00:17
And i want to know what's this angle.
00:21
Okay, so i have three sides.
00:23
I want to find an angle.
00:25
That is a law of cosine's problem.
00:29
Law of cosine says c squared equals a squared plus b squared minus 2ab cosine c.
00:39
Since i want to solve for the angle, i'm going to rewrite the formula to isolate cosine c.
00:46
So i'm going to subtract a squared and b squared.
00:52
Then i'm going to divide everything by negative 2ab...