Answer:
[tex]cosB=\frac{a}{c}[/tex]
Step-by-step explanation:
The cosine ratio is [tex]cosineX=\frac{adjacent}{hypotenuse}[/tex] for the given angle. In this case, the angle is B. So you need the side adjacent the angle B (next to) that is NOT the hypotenuse. You also need the hypotenuse. S you would need :
[tex]cosB=\frac{a}{c}[/tex]
You can remember the ratios by using SOH-CAH-TOA.
Sine=Opposite/hypotenuse
Cosine=adjacent/hypotenuse
Tangent=opposite/adjacent
