The arithmetic mean of x and y is 10 and their geometric mean is 8, what is the value of x and y?
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Given:
The arithmetic mean of x and y is 10 and their geometric mean is 8
To find:
What is the value of x and y?
Solution:
From given, we have,
The arithmetic mean of x and y is 10 and their geometric mean is 8
Now consider,
The arithmetic mean of x and y is 10
⇒ (x + y)/2 = 10
x + y = 20 ...... (1)
y = 20 - x ...... (2)
The geometric mean of x and y is 8
⇒ √xy = 8
square on both the sides,
xy = 8²
xy = 64...... (3)
substitute the value of equation (2) in the equation (3)
x (20 - x) = 64
20x - x² = 64
x² - 20x + 64 = 0
(x - 4) (x - 16) = 0
x = 4, 16
when x = 4,
xy = 64 ⇒ y = 64/x ⇒y = 64/4 ⇒ y = 16
∴ y = 16
when x = 16,
xy = 64 ⇒ y = 64/x ⇒y = 64/16 ⇒ y = 4
∴ y = 4
The values of x and y are 4 and 16