Question

Cosine rule equation ​

Answer 1

79.2 degrees (to 1 dp)

Explanation:

the cosine rule to find an angle is
`cos^(-1) ((a^(2)+b^(2)-c^(2) )/(2bc) )`

here, c is the side opposite to the angle you want to find which in this case is 9 and a and b would be the other side lengths which are 8 and 7 so,

`cos^(-1) ((8^(2)+7^(2)-9^(2) )/(2*8*7) )` (* means multiply)

simplify this and you'll get

`cos^(-1) ((3)/(16) )`

put this into your calculator and you'll get approximately 79.2 degrees

Answer 2

the equation for the cosine rule is:
a^2 = b^2 + c^2 – 2bc cos(A).
if you want to find out the angle, it is:
cos(A) = b^2 + c^2 - a^2 / 2bc.