`frac{7x^2-14x-5}{15}=frac{(2x+1)^2}{5}-frac{(x-1)^2}{3}`
`<=>frac{7x^2-14x-5}{15}=frac{3(2x+1)^2}{15}-frac{5(x-1)^2}{15}`
`=>7x^2-14x-5=3(2x+1)^2-5(x-1)^2`
`<=>7x^2-14x-5=3(4x^2+4x+1)-5(x^2-2x+1)`
`<=>7x^2-14x-5=12x^2+12x+3-5x^2+10x-5`
`<=>7x^2-14x-5=7x^2+22x-2`
`<=>7x^2-7x^2-14x-22x=-2+5`
`<=>-36x=3`
`<=>x=1/12`
Vậy phương trình có nghiệm `S={1/12}`