Pada segi tiga ABC diketahui panjamg BC=3 cm .AC=2 cm dan sin A =1/2. maka nilai cos B adalah...
subebe
BC/ sin A = AC / sin B 3 / 1/2 = 2 / sin B 3 sin B = 1 sin B = 1/3 sin² B + cos²B = 1 (1/3)² + cos² B = 1 1/9 + cos² B = 1 cos² B = 1 - 1/9 cos² B = 8/9 cos B = (2√2 / 3)
3 / 1/2 = 2 / sin B
3 sin B = 1
sin B = 1/3
sin² B + cos²B = 1
(1/3)² + cos² B = 1
1/9 + cos² B = 1
cos² B = 1 - 1/9
cos² B = 8/9
cos B = (2√2 / 3)