Answer:
AC = 13.9 cm.
Step-by-step explanation:
See the attached diagram.
Draw a perpendicular on AD from B which is BE.
Now, CD = BE
Now, Δ ABE is a right triangle and
AB² = BE² + AE² {Applying Pythagoras Theorem}
⇒ 11² = BE² + (AD - DE)²
⇒ 11² = BE² + (11 - 4)² {Since CB = DE = 4 cm}
⇒ 11² = BE² + 7²
⇒ BE² = 11² - 7² = 72
⇒ CD² = 72
Now, Δ ACD is a right triangle and
AC² = CD² + DA² {Applying Pythagoras Theorem}
⇒ AC² = 72 + 11² = 193
⇒ AC = 13.89 ≈ 13.9 cm