`b, 9x^2 - 12x + 4 - 5x^2 + 45 = 4x^2 + 2x - 5`
`4x^2 - 12x + 49 = 4x^2 + 2x - 5`
`54x = 14`
`x = 7/27.`
`c, 9x^2 - 3x^2 - 2x + 15x + 10 = 4`
`<=> 6x^2 + 13x + 6 =0`
`<=> x = -3/2` hoặc `x=-2/3`
`d, 9x^2 - 24x + 16 + 8 = 64`
`9x^2 - 24x - 40 = 0`
`x = (4+-2sqrt14)/3`.