- 数学题已知x,y是实数,且2^x+3^y=<(2^
- 已知x,y是实数,且2^x+3^y=<(2^-y)+(3^-x). 则x,y满足:A.x+y>=0 B.x+y<=0 .x-y>=0 D.x-y<=0
- 已知x,y是实数,且2^x+3^y≤(1/2)^y+(1/3)^x. 则x,y满足:
A.x+y≥0 B.x+y≤0 C.x-y≥0 D.x-y≤0
由已知得:2^x-(1/3)^x≤(1/2)^y-3^y
即 2^x-(1/3)^x≤2^(-y)-(1/3)^(-y)
∵函数z=2^t-(1/3)^t 是增函数
∴当2^x-(1/3)^x≤2^(-y)-(1/3)^(-y)时有:x≤-y
∴x+y≤0
选 B