Question

What’s the correct answer

Answer 1

(A) 79°

Explanation:

We can use law of cosine.

c²=a²+b²-2ab*cos(α)

14²=11²+11²-2*11*11*cos(A)

14²=2*11²-2*11²cos(A)

14²-2*11²=-2*11²cos(A)

-46= - 2*(121)*cos(A)

cos(A)= 46/242

arccos(46/242)=79°

Answer 2

79°

Explanation:

Using the cosine rule in ΔABC

cosA =
`(b^2+c^2-a^2)/(2bc)`

with a = 14, b = 11, c = 11, then

cosA =
`(11^2+11^2-14^2)/(2(11)(11))` =
`(46)/(242)`

A =
`cos^(-1)`(
`(46)/(242)`) ≈ 79°