1.

Solve `(x^(2) - 2x)^(2) - 23 (x^(2) - 2x) + 120 = 0`

Answer» Let us assume that `x^(2) - 2x = y`
`rArr` The given equation reduced to a quadratic equation in y.
That is, `y^(2)- 23 + 120 = 0`
`rArr y^(2) - 15y - 8y + 120 = 0`
`rArr y(y-15) - 8 (y-5) = 0`
`rArr (y-8) (y-15) = 0`
`rArr y - 8 = 0` (or) `y - 15 = 0`
`rArr y = 8`(or) `y = 15`
But `x^(2) - 2x = y`
When `y = 8, x^(2) - 2x = 8`
When `y = 8, x^(2)- 2x = 8`
`rArr x^(2) - 2x - 8 = 0`
`rArr x^(2) - 4x + 2x - 8 = 0`
`rArr x(x-4) +2(x-4) = 0`
`rArr (x+2) (x-4) = 0`
`rArr x+2 = ` (or) `x - 4 = 0`
`rArr x = - 2` (or) `x = 4`
When `y = 15, x^(2)- 2x = 15`
`rArr x^(2) - 2x - 15 = 0`
`rArr x^(2)- 5x + 3x - 15 = 0`
`rArr x(x-5) + 3(x-5) = 0`
`rArr (x-5) (x+3)= 0`
`rArr x- 5 = 0` (or) `x + 3 = 0`
`rArr x= 5` (or) `x =-3`
`:. x = - 2,-3, 4` and 5 are the required solutions of the given equation .


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