# Math Help - Law of cosine

1. ## Law of cosine

My teacher got 7.30, but I can't seem to get the right anwser.

How do I solve for a?

I get 14 when I solve it

a^2=11^2+7^2-2(11)(7)cos62
a^2=121+49-2(77)cos62
a^2=270-154cos62
a^2=197.70
square root of a^2 = Square root of 197.70
a=14.06

2. Hello, live504!

I don't agree with either of you . . .

My teacher got 7.30, but I can't seem to get the right answer.

I get 14 when I solve it

$a^2 \:=\:11^2+7^2-2(11)(7)\cos62$

$a^2\:=\:121+49-2(77)\cos62$

$a^2\:=\:{\color{red}270}-154\cos62\quad\hdots\quad {\color{blue}121 + 49 \:=\:170}$

$a^2\:=\:197.70$

$a \:=\:\sqrt{197.7} \;\approx\;14.06$

$a^2 \;=\;170 - 154\cos62^o \;\approx\;97.70$

Therefore: . $a \;=\;\sqrt{97.70} \;\approx\;9.88$