`c)`
`(x^2 - 9)^2 - (x+3)(x-3)(x^2 + 9)`
`= [ (x^2)^2 - 2 . x^2 . 9 + 9^2] - (x^2 - 3^2)(x^2 + 9)`
`= (x^4 - 18x^2 + 81) - (x^2 - 9)(x^2 + 9)`
` = x^4 - 18x^2 + 81 - [(x^2)^2 - 9^2]`
`= x^4 - 18x^2 + 81 - (x^4 - 81)`
`= x^4 - 18x^2 + 81 - x^2 + 81`
` = -18x^2 + 162`
`d)`
`(x^2 + x - 3)(x^2 - x +3)`
` = (x^2 + x-3)[x^2 - (x-3)]`
` = (x^2)^2 - (x-3)^2`
` = x^4 - (x^2 - 6x + 9)`
`= x^4 - x^2 + 6x - 9`
``
`d)`
`(x^2 + x-3)[ x^2 - (-x) + 3]`
`= (x^2 + x-3)(x^2 + x + 3)`
`= (x^2 + x)^2 - 3^2`
` = [(x^2)^2 + 2 . x^2 . x + x^2] - 9`
`= x^4 + 2x^3 + x^2 - 9`
