The given triangle is a right angled triangle. So we can use the pythagorean theorem to solve this.
Hypotenuse = 14 cm
Altitude = 7 cm
Base = x cm
Using pythagorean theorem,
Hypotenuse² = Base² + Altitude²
14² = x² + 7²
14² - 7² = x²
196 - 49 = x²
147 = x²
√147 = x
12.124 = x (approx.)
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Hope it helps ⚜