Question

A scalene triangle has the lengths 6, 11, and 12. Keyla uses the law of cosines to find the measure of the largest angle. Complete her work and find the measure of angle Y to the nearest degree. 1. 122 = 112 + 62 − 2(11)(6)cos(Y) 2. 144 = 121 + 36 − (132)cos(Y) 3. 144 = 157 − (132)cos(Y) 4. −13 = −(132)cos(Y)

Answer 1

`Y\approx 84^\circ $(to the nearest angle)`

Explanation:

The lengths of the sides of the scalene triangle are 6, 11, and 12.

We want to use the law of cosines to find the largest angle.

Note that the largest angle is always opposite the largest side.

Therefore:

`1. 12^2 = 11^2 + 6^2-2(11)(6)\cos(Y) \\\\2. 144 = 121 + 36-(132)\cos(Y) \\\\3. 144 = 157 - (132)\cos(Y) \\\\4. -13 = -(132)\cos(Y)\\\\\\5. \cos(Y) = (-13)/(-132) \\\\6. Y = \arccos \left ( (13)/(132)\right)\\\\7. Y=84.35^\circ\\\\8. Y\approx 84^\circ $(to the nearest angle)`

The largest angle is 84 degrees to the nearest angle.