`A)x:0,25+x:0,5(x+x:0,01)=215`
`x*4+x*2(x+x*100)=215`
`<=>x*4x+x*2+101x=215`
`<=>4x+202xx=215`
`<=>4x+202x^2-2515=0`
`<=>x=-(2-3√4826)/202` hoặc `-(2+3√4826)/202`
`B)17,25-(0,5×x:2-4,2)=15`
`<=>0,5*x:2-4,2=2,25`
`<=>0,5*x:2=6,45`
`<=>0,5*x=12,9`
`<=>x=25,8`
Vậy ..............