Range Rover!! :p

Algebra Level 3

If the range of the function f(x) = x + 1 + 3 x \sqrt { x+1 } +\sqrt { 3-x } is [ a , b c ] [a,b\sqrt { c } ] , find a+b+c , where a,b,c are Integers and c is square free


The answer is 6.

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

2 solutions

James Wilson
Jan 9, 2021

The minimum and maximum of a differentiable function occur either at the endpoints of its domain or where the derivative equals zero. The domain of f ( x ) f(x) is { x 1 x 3 } \{x|-1\leq x \leq 3\} . f ( x ) = 1 2 x + 1 1 2 3 x f'(x)=\frac{1}{2\sqrt{x+1}}-\frac{1}{2\sqrt{3-x}} , which is defined on the interval ( 1 , 3 ) (-1,3) . There is one solution to f ( x ) = 0 f'(x)=0 , namely, x = 2 x=2 . That gives us 3 points to check: the points corresponding to x = 1 , 2 , 3 x=-1,2,3 . The minimum = 2, which occurs at x = 1 , 3 x=-1,3 . The maximum = 2 2 2\sqrt{2} , which occurs at x = 2 x=2 .

Abhishek Chopra
May 5, 2015

The Minimum value of this function is at x=-1 and x=3 where f(X) becomes 2 and maximum when x=1 where f(x) becomes 2 *2^1/2 therefore a+b+c=6

why do u think so?

Sriram Vudayagiri - 6 years, 1 month ago

Log in to reply

We need to keep in mid that we cant have a real expression when we square root a negative integer hence for the minimum value x+1 and 3-x both equal to 0.As they cant be negative.And same for the Maximum value where 3-x and x+1 are both greater than 0.

Abhishek Chopra - 6 years ago

Log in to reply

Why is that the minimum will occur at x = -1 or 3? Why cant it occur between them? How can you be so sure?

Sriram Vudayagiri - 6 years ago

Log in to reply

@Sriram Vudayagiri This is Because (x+1)^1/2 and (3-x)^1/2 is always greater than or equal to 0. Hence the function is minimum when either of them is 0.

Abhishek Chopra - 6 years ago

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...