- #1

Gringo123

- 141

- 0

In a triangle...

angle A = 35

^{0}

side b = 7 cm

side c = 3 cm

I need to find side a which is the side opposite angle A.

The formaula to use is -a

_{2}= b

_{2}+ c

_{2}- 2bc cos A

so, with the figures plugged in that comes out as...

a

_{2}= 7

_{2}+ 3

_{2}- 2 x 3 x 7 cos 35

which comes to...

a

_{2}= 58 - 42 cos 35

SO FAR, I KNOW THAT IS CORRECT. I seem to have made the mistake at this point. I multiplied 16 (58-42) by cos 35 and took the square root of the answer, which gave me 3.62 cm.

However, apparently the right answer is 4.86 cm.

What did I do wrong?