Did you make a sketch of y = (2x-10)^(1/2) ?
Let Q be any point on the curve
then Q can be labelled (x, (2x-10^1/2 )
slope of oQ = (2x-10)^1/2 / x
let the angle made by OQ with the x-axis be ě
taně = y/x = (2x-10)^1/2 / x
sec^2 ě dě/dx = (x(1/2)(2x-10)^(-1/2)(2) - (2x-10)^(1/2) (1) )/x^2 using the quotient rule
for a max of ě , dě/dx = 0
so (x(1/2)(2x-10)^(-1/2)(2) - (2x-10)^(1/2) (1) )/x^2 = 0
(x(1/2)(2x-10)^(-1/2)(2) - (2x-10)^(1/2) (1) ) = 0 , we can ignore the denominator.
x/(2x-10)^(-1/2) - (2x-10)^1/2 = 0
x/(2x-10)^1/2 = (2x-10)^1/2
x = 2x-10 , after cross-multiplying
x = 10
so Q is (10, 10^1/2) or (10, √10)
at x=10, taně = √10/10 = .31622 , ě = 17.548░
at x = 10.1 , taně = √10.2/10.1 = .3162 ě = 17.547 ░ -- a bit smaller
at x = 9.9 , taně = √9.8/9.9 = .3162116, ě = 17.547 -- again a bit smaller than at x=10
my answer looks good!
thank you very much, I understand my mistake!
So, we want to maximize
t = arctan(sqrt(2x-10)/x)
t' = -(x-10)/[(sqrt(2x-10)/x)^2 + 1)*x^2 * sqrt(2x-10)]
All that junk in the bottom is never zero when x>5, so we just have to find where x-10 = 0
well, duh: x=10
So, Q = (10,√10)
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