u_(n+1) = u_n −u_n ^3 , u_0 ∈]0,1[
v_n = (1/u_(n+1) ^2 )−(1/u_n ^2 ) = f(u_n ^2 ) ; f(x) = ((2−x)/((1−x)^2 ))
v_n converges to 2, v_n is decreasing
. show that v_n ≥ 2
x_n =(1/(n+1))Σ_(m=0) ^m (v_m )
. show that x_0 ≥x_n ≥v_n
. show that x_n is decreasing and lim_(n→∞) x_n = l ≥2
. show that 2x_(n+1) −x_n ≤v_(n+1) and deduce l
. express x_(n+1) −x_n interms of u_n
. deduce lim_(n→∞) nu_n ^2
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