How do you find #lim_(x->0^+)(sinx)^x#?

How do you find #lim_(x->0^+)(sinx)^x#?

1 Answer
Jan 18, 2018

#lim_(xrarr0^+)sinx^x=1#

Explanation:

#lim_(xrarr0^+)sinx^x=?#

#sinx^x=e^(ln(sinx)^x)=e^(xln(sinx))#

#= lim_(xrarr0^+)e^(xln(sinx))# #(1)#

You see that we still have problem and can't calculate the limit at it's current form as #ln0# is not defined.
Let's study this limit seperately

#lim_(xrarr0^+)ln(sinx)=#

Set

#sinx=u#
#x->0^+#
#u->0^+#

#=# #lim_(urarr0^+)lnu=-oo#

graph{lnx [-10, 10, -5, 5]}

#lim_(xrarr0^+)xln(sinx)=lim_(xrarr0^+)ln(sinx)/(1/x)=_(DLH)^(((-oo)/(+oo)))#

#lim_(xrarr0^+)(((sinx)')/sinx)/(-1/x^2)=-lim_(xrarr0^+)(cosx/sinx)/(1/x^2)=-lim_(xrarr0^+)((x^2cosx)/sinx)#

#x->0^+#

#x>0#

#=# #-lim_(xrarr0^+)(cosx)/(sinx/x*1/x)=^((1/(1*(+oo)))# #0#

  • because

#lim_(xrarr0^+)cosx=cos0=1#

#lim_(xrarr0^+)sinx/x=1#

#lim_(xrarr0^+)(1/x)=^((1/(0^+))# #+oo#

Now if in #(1)# i set:

#y=xln(sinx)#

#x->0^+#
#y->0#

and #(1)# now becomes:

#lim_(yrarr0)e^y=e^0=1#

As a result,

#lim_(xrarr0^+)sinx^x=1#