theorem Th55: :: SQUARE_1:55

for a, b being Real st - 1 <= a & a <= 1 & - 1 <= b & b <= 1 holds
( (- b) * (sqrt (1 + (a ^2))) <= sqrt (1 + (b ^2)) & - (sqrt (1 + (b ^2))) <= b * (sqrt (1 + (a ^2))) )