Originally Posted by
waxer1987 I used the cosine law, maybe i'm doing it wrong. This is what I did.
my sketch
A------------------D For some reason I can't draw the pic , but D and C are connected as well as A and B. (parrallelogram)
/ /
/ /7cm
/ /
B-----------------C
9cm
With a line from A to C which is 12.0cm.
And a line from B to D which I need to figure out.
I used Angle BDC
c^2 = b^2 + d^2 - 2bd cosC
144 = 130 - 126cosC
130-144 = -126cosC Should be 144 - 130 = -126 cos C
-14 = -126cosC
-14/-126 = cosC
0.1111... = cosC
c= cos^-1(0.1111...) So cos C = -0.1111...
c= 83 degrees C = 96 degrees
but how can it be 83 degrees if its obtuse? what did i do wrong? did I draw it wrong?