Given x + y = m, a + B = n, then the maximum value of AX + by is?

Given x + y = m, a + B = n, then the maximum value of AX + by is?

And a & sup2; + B & sup2; = n. known by the caucauchy inequality, Mn = (X & sup2; + Y & sup2; (A & sup2; + Y & sup2; (A & sup2; + B & sup2;)) (A & sup2; (A & sup2; (a & sup2; + B & sup2;) (A & sup2; (A & sup2; (A & sup2; + B & sup2;) (A & sup2; (A & sup2; (A & sup2; (X & sup2; + B & sup2; + B & sup2; + B & sup2;) (A & sup2; (A & sup2; (A & sup2; + A & sup2; + A & sup2; + A & sup2; + A & sup2; a & sup2; + A & sup2; a & sup2; a & sup2; + A & sup2; (A & sup2; a & sup2; + A & sup2; (A & sup2; a & sup2; a sup2; Y & sup2; = (AX + by) & sup2; + (ay-bx) & sup2; (AX + by) & sup2;. The equal sign is obtained only when ay-bx = 0, where (AX + by) = √ (MN).]