Answer:
2.1
Step-by-step explanation:
a²=b²+c²-2bc cos A
a²=5²+6²-2*5*6* cos(20)
a²= 25+36-60* cos (20)
a²= 61-60*0.939
a²= 61-56.382
a²= √4.618
a= 2.15
