Bonjour,
x²<1 <=> x²-1<0 <=> (x-1)(x+1)<0
x - ∞ -1 1 +∞
x-1 - - +
x+1 - + +
(x-1)(x+1) + - +
Et donc x²<1 <=> (x-1)(x+1)<0 <=> x∈ ]-1,1[
