## anonymous one year ago In triangle ABC, a = 3, b = 5, and c = 7. Find the approximate value of angle A. 22° 38° 142° 158°

1. johnweldon1993

We can use the law of cosine here we know $\large a^2 = b^2 + c^2 - 2bc \times cos(A)$ So since we want to solve for A we need to rearrange this into $\large A = \arccos(\frac{a^2 - b^2 - c^2}{-2bc})$ So just plug in everything you have and solve

2. anonymous

what is arccos

3. johnweldon1993

the inverse cosine function also known as $$\large cos^{-1}$$

4. anonymous

okay and i just got .92

5. anonymous

btw i dont have an actual calculator

6. johnweldon1993

The 0.92 is what you get when you do everything in the parenthesis...now you just need the inverse cosine of that Which, since you dont have a calculator...comes out to 21.786

7. johnweldon1993