Question

considerando0<a <90sena=2/3 calcule cosa​

Answer 1

cosa= √1-sen²a

cosa= √1-(2/3)²

cosa= √1-(4/9)

cosa= √9/9- (4/9)

cosa=√(5/9)

cosa= √5/√9

cosa= √5 /3

Answer 2

relação fundamental:

( sen a ) 2 + ( cos a) 2 = 1

( 2 / 3 ) 2 + ( cos a ) 2 = 1

4 / 9 + ( cos a ) 2 = 1

( cos a ) 2 = 1 - 4 / 9

( cos a ) 2 = 9 / 9 - 4 / 9

( cos a ) 2 = 5 / 9

cos a = √5/9

cos a = √5 / 3