(a-b)(a+b)=a²-b²=|a|²-|b|²=1,于是|b|=√2/2,于是|a||b|=√2/2cosθ=ab/(|a||b|)=(1/2)/(√2/2)=√2/2,得θ=π/4………………|a+b|²=(a+b)²=a²+2ab+b²=|a|²+2ab+|b|&...