Answer:
x ≈ 2.76
Step-by-step explanation:
Using the tangent ratio in the right triangle
tan78° = [tex]\frac{opposite}{adjacent}[/tex] = [tex]\frac{AB}{BC}[/tex] = [tex]\frac{13}{x}[/tex] ( multiply both sides by x )
x × tan78° = 13 ( divide both sides by tan78° )
x = [tex]\frac{13}{tan78}[/tex] ≈ 2.76 ( to 2 dec. places )
