If you are given that [math]a[/math], [math]b[/math], [math]c[/math], and [math]d[/math] are all positive real numbers, and that [math]a>b[/math] and [math]c>d[/math], how do you demonstrate that [math]ac > bd[/math]?
Can it be solved: [math]a+b=8;c-d=6;a+c=13;b+d=8[/math] ?