I need help with this question involving law of cosines, etc.? Will give medal & fan.
"Use the law of cosines to find the value of 2 * 4 * 5 cos theta"
A. 40
B. -40
C. 20
D. 37

I used the formula C = cos^-1 (a^2 + b^2 - c^2 / 2ab) and got 108.21, which obviously isn't the answer /:

Question

I need help with this question involving law of cosines, etc.? Will give medal & fan.
"Use the law of cosines to find the value of 2 * 4 * 5 cos theta"
A. 40
B. -40
C. 20
D. 37

I used the formula C = cos^-1 (a^2 + b^2 - c^2 / 2ab) and got 108.21, which obviously isn't the answer /:

loser66 · Answer

I don't get the question. Do you have a pic? what is a, b , c and 2, 4, 5 relationship?

anonymous · Answer

|dw:1401147756307:dw|

loser66 · Answer

I think you apply the wrong formula
|dw:1401148213560:dw|

anonymous · Answer

Ohh okay so that's the formula I was supposed to use?

loser66 · Answer

you apply the right formula, just put the wrong label on it. The law of cos is talking about the angle C and the 2 adjoint legs of it, I mean|dw:1401148622820:dw|

loser66 · Answer

while your pic |dw:1401148703016:dw|