In triangle PQR, side p is 19m, side r is 7m, side q is 15m. How do you find the measure of angle R?

1 Answer
sankarankalyanam
Apr 11, 2018

color(brown)("Measure of " hatR = 45.93^@

Explanation:

![http://www.dummies.com/education/math/trigonometry/laws-of-sines-and-cosines/](useruploads.socratic.org)

Applying the law of cosines,

cos R = (r^2 - p^2 - q^2 ) / (-2 pq)

cos R = (p^2 + q^2 - r^2) / (2 pq) = (19^2 + 7^2 - 15^2) / (2 * 19 * 7)

cos R = 0.6955 " or " hat R = cos ^-1 (0.6955) ~~ 45.93^@

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