In triangle ABC, ∠CAB=40∘, AC = 6 cm, AB = 7 cm. The length BC is equal to_____. [sin 40∘=0.67, cos 40∘=0.76]
4.55 m
Draw CD⊥AB
In △ADCsin40∘=CDAC0.64=CD6CD=6×0.64=3.85 mcos40∘=ADAC0.76=AD6AD=6×0.76AD=4.56 mFrom figure, we can see thatDB=AB−ADDB=7−4.56DB=2.44 mIn right-angled triangle CDB
BC2=BD2+DC2BC2=(2.44)2+(3.85)2BC2=5.95++17.82BC2=20.77BC=4.55 m