Explications étape par étape:

a. sin83° = 2,1/ET

ET *sin83° = 2,1

ET = 2,1/sin83°

b. cos P = SP/RP

cos 19° = 5/RP

RP * cos 19° = 5

RP = 5/cos19

RP = environ 5,3 cm

c. tan P = RS/SP

tan19° = RS/5

5 * tan19° = RS

Donc RS =environ 1,72cm