How do you solve #x^4-81=0#?

1 Answer
Sep 29, 2015

Answer:

#color(blue)(x=+-3#

Explanation:

#x^4 -81=0#

By property
#color(blue)(a^2-b^2=(a-b)(a+b)#

Similarly we can rewrite the expression given :

#x^4 -81=(x^2)^2-(9^2)#

#=color(blue)((x^2-9)(x^2+9)#

Equating the factors to zero:

1) #x^2-9=0#
#x^2=9#
#color(blue)(x=+-3#

2) #x^2+9=0#
#x^2=-9#
This case is not applicable as we cannot take the root of a negative number.