Question

A triangle has sides of length 5, 8, and 10. What is the measure of its largest angle?

Answer 1

Use the law of cosines

Answer 2

I did but can not seem to get the right answer

Answer 3

\[10^2=5^2+8^2-2(5)(8)\cos A\]
\[100-89=80\cos A\]
\[\frac{11}{80}=\cos A\]=.1375
\[\cos^{-1} (.1375)=82.1^{o}\]

Answer 4

That's what I got, but the back of the book said it was 97.9 @Mertsj

Answer 5

\[100-89=-80\cos A\]

Answer 6

You do get what the book says. Mert just forgot the little negative sign

Answer 7

How is it the same as what the book says?

Answer 8

try using the calculator

Answer 9

arccos(-11/80)

Answer 10

I did so if I use the negative I will get the right answer?

Answer 11

yes