Question

What’s the correct answer

Answer 1

79°

Explanation:

Use the cosine law:

`BC^2=AC^2+AB^2-2(AC)(AB)\cos A`

We have

BC = 14, AC = 11 and AB = 11. Substitute:

`14^2=11^2+11^2-2(11)(11)\cos A\\\\196=121+121-242\cos A\\\\196=242-242\cos A\qquad\text{subtract 242 from both sides}\\\\-46=-242\cos A\qquad\text{divide both sides by (-242)}\\\\\cos A=(-46)/(-242)\\\\\cos A=(23)/(121)\\\\\cos A\approx0.1901\to m\angle A=79^o\\\\(\text{look at the table on a picture})`