InverseCosine
The last inversetrigonometricratio is arccosine(oftenshortenedto arccos).The samerulesapplyfor arc-
cosineas applyfor all otherinversetrigonometricfunctions.You can use it to isolatea variablefor an angle
measurement,but you mustperformthe operationon both sidesof the equation.Whenyou knowthe arc-
cosinevalue,use a tableor a calculatorto find the measureof the angle.
Example 5
Solvefor if.You can use the inverseof cosine,arccosine,to find this value.Thenuse your calculatorto find the arccosineof.Example 6
Whatis the measureof in the trianglebelow?First identifythe propertrigonometricratio relatedto that can be foundusingthe sidesgiven.The
cosineusesthe adjacentside and the hypotenuse,so it will be relevanthere.
Now use the arccosineto isolatethe valueof.Finallyuse your calculatoror a tableto find the arccosineof