如果img class=kfformula src=zzximg/20190808/1565251013539366.png data-latex=ab/,那么下列不等式正确的是( )
①
img class=kfformula src=zzximg/20190808/1565251013738499.png data-latex=a-2b-2/
②
img class=kfformula src=zzximg/20190808/1565251013586057.png data-latex=\frac {1} {2}a\frac {1} {2}b/
③
img class=kfformula src=zzximg/20190808/1565251013931183.png data-latex=-3a-3b/
④
img class=kfformula src=zzximg/20190808/1565251013130324.png data-latex=5a5b/