how are they getting 9771102cosB from 1521922922 1929cosB Vi

how are they getting -977=-1102cosB from (15)^2=(19)^2+(29)^2-2 (19)(29)cosB?

View an Example Solve the triangle le number as needed To solve or the measure of angle B. use the law of cosines showm below. gle B? 2ac cos B Substitute the known values in the formula and simplity b2 a2 +c2 2ac B cos 20190029)cos B Substitute 977 1102cos B 0,88657 cos B Press Continue to see more. it fields and then d 5 Parts remaining

Solution

15²=19²+29²-2(19)(29)cosB

225=361 +841-1102 cos B

225=1202 -1102 cos B

subtracting both sides 1202

-977=-1102 cos B