`a,(x-280):35=56:x`
`<=>(x-280)*1/35=56*1/x`
`<=>x-280=56/x`
`<=>x^2(x-280)=1960`
`<=>x^2-280x=1960`
`<=>x^2-280x-1960=0`
`<=>x=14(10+√110)` hoặc `x=14(10-√110)`
Vậy `x=14(10+√110)` hoặc `x=14(10-√110)`
`b,697:[(15x+364):x]=17`
`<=>697*1/[(15x+364)*1/x]=17`
`<=>(697*x)/(15x+364)=17`
`<=>(697x)/(15x+364)=17`
`<=>17(15x+364)=697x`
`<=>26x=364`
`<=>x=14`
Vậy `x=14`