1)甲:(80a+80b)/(80+80)=(a+b)/2 (元)
乙:(80+80)/(80/a+80/b)=2ab/(a+b) (元)
2)(a+b)/2 -2ab/(a+b)
=[(a+b)²-4ab]/[2(a+b)]
=(a-b)²/[2(a+b)]
∵(a-b)²≥0
(a-b)²/[2(a+b)]≥0
∴(a+b)/2≥2ab/(a+b)
因此,乙的方式更合算.
1)甲:(80a+80b)/(80+80)=(a+b)/2 (元)
乙:(80+80)/(80/a+80/b)=2ab/(a+b) (元)
2)(a+b)/2 -2ab/(a+b)
=[(a+b)²-4ab]/[2(a+b)]
=(a-b)²/[2(a+b)]
∵(a-b)²≥0
(a-b)²/[2(a+b)]≥0
∴(a+b)/2≥2ab/(a+b)
因此,乙的方式更合算.