#color(blue)(a^2 - b^2 = (a+b)(a-b)#
#(x^2-9) = (x+3)(x-3)#
the expression given is:
#1/(x+3) + 1/(x-3) = 1/(x^2-9)#
#1/(x+3) + 1/(x-3) = 1/((x+3)(x-3)#
#(1.(x-3))/((x+3)(x-3)) + (1.(x+3))/((x-3)(x+3)) = 1/((x+3)(x-3)#
#((x-3)+ (x+3))/((x+3)(x-3)) = 1/((x+3)(x-3))#
#(2x)/cancel(x^2-9) = 1/cancel(x^2-9)#
#2x = 1#
# x =color(blue)( 1/2# is the solution for the expression.