# Find k if the function f(x) is continuous at x=4.f(x)=cos pi/x, x>=4 f(x)=2square root x, x<4

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Student Comments

giorgiana1976 | Student

Since you've not specified where is placed k, we'll assume that f(x) = k`sqrt(x)`

For a function to be continuous at a point x=a, it must obey the following rules:

1) f(a) must exist

2) lim f(x) is finite

x-> a

3) lim f(x) = f(a)

x-> a

Now, we'll determine the value of k, knowing that the function is continuous.

lim cos `pi` /x = lim k`sqrt(x)` = f(4)

x->4 x->4

lim cos `pi` /x = cos `pi` /4 = sqrt2/2

x->4

lim k`sqrt(x)` = ksqrt4 = 2k

x->4

f(4) = cos ` ` /4 = sqrt2/2

We'll re-write the 3rd condition of continuity:

sqrt2/2 = 2k => k = sqrt2/4

**The value of k for the given function to be continuous is k = sqrt2/4.**