Question

Really short Question; Please help and Show your Work! I would rate you 5 stars or anything you like

Answer 1

Answer:

  about 94.41°

Step-by-step explanation:

The Law of Cosines can be used to find an angle in a triangle with three sides given.

Setup

The law of cosines relation generally relates the side opposite the angle to the other measures in the triangle:

  r² = p² +q² -2pq·cos(R)

Solution

We want to find the measure of angle R, so we solve the equation for that:

  2pq·cos(R) = p² +q² -r² . . . . . . add 2pq·cos(R)-r²

  cos(R) = (p² +q² -r²)/(2pq) . . . . divide by the coefficient of the cosine

We can fill in the given side lengths at this point:

  cos(R) = (13² +10² -17²)/(2·13·10) = -20/260 = -1/13

Then the angle can be found using the arccos function:

  R = arccos(-1/13) ≈ 94.41°

The measure of angle R is about 94.41°.

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Additional comment

When you have done a few of these, you recognize that the angle opposite side 'c' is ...

  C = arccos((a² +b² -c²)/(2ab))

A calculator can make short work of this. The second attachment shows the evaluation of this expression with a=10, b=13, c=17. The calculator angle mode is set to degrees. The arccos function is the 2ND function of the Cos key.