Find the range of the function \(m(x) = \sqrt{x + 5} + \sqrt{20 - x}.\)
x has these restrictions
-5 ≤ x ≤ 20
When x = -5 m(x) = 5
When x = 20 m (x) = 5
So....this function must have a max between x = -5 and x = 20
To find the x value that maximizes this function....we can use Calculus
m ' (x) = (1/2) (1/2)
___________ + ____________
(x + 5)^(1/2) (20 - x)^(1/2)
Set this to 0 and solve for x
1 1
___________ + __________ = 0
(x + 5)^(1/2) (20 - x)^(1/2)
1 - 1
___________ = ___________ square both sides
( x + 5)^(1/2) (20 - x)^(1/2)
1 1
_______ = ______ cross- multiply
(x + 5) (20 -x)
20 - x = x + 5
15 = 2x
7.5 = x this x maximizes the function
So when x =7.5 we can fnd y as
(7.5 + 5)^(1/2) + ( 20 - 7.5)^(1/2) =
(12.5)^(1/2) + (12.5)^(1/2) =
2 ( 12.5)^(1/2) =
2 ( 25/2)^(1/2) =
2 * 5 / √2 =
5√2
So the range is [ 5 , 5√2 ]