Answer:
4√10
Step-by-step explanation:
From the geometric mean theorem, when we have this type of rectangle with a height of say "x" and left and right distances to this height as "a" and "b" respectively, then the theorem says that;
x/a = b/x
Applying it to this question;
Altitude is "m"
Left side measurement is 8
Right side measurement is 20
Thus;
m/8 = 20/m
Cross multiply to get;
m² = 160
m = √160
m = √(16 × 10)
m = 4√10
