Question

what i did wrong ........the picture is answer ...and question is 1. factorise x^3-3x^2-9x-5

Answer 1

x³ - 3x² - 9x - 5

=> x³ + x² - 4x² - 4x - 5x - 5


[ -3x² = x² - 4x² and -9x = -4x - 5x ]



=> x²(x + 1 ) - 4x( x + 1 ) - 5(x + 1 )


=> ( x + 1 ) ( x² - 4x - 5 )

=> ( x + 1 ) [ x² - ( 5 - 1 ) x - 5 ]

=> ( x + 1 ) (x² - 5x + x - 5 )

=> ( x + 1 ) [ x( x - 5 ) + ( x - 5 )]



=> ( x + 1 ) ( x + 1 ) ( x - 5)


They are factors, Match your solution.




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Answer 2

ʜᴇʟʟᴏ ᴍᴀᴛᴇ!

Let's take 5 as value of x, as you did

p(x) = (5)³ - 3(5)² - 9(5) - 5
0 = 125 - 75 - 45 - 5
0 = 0

So, ( x - 5 ) is factor of p(x)

Now, Divide the p(x) by ( x - 5 ),

Here, I have attached an image. In attatchment you will get full solution.

Answer is ( x - 5 )( x + 1 )( x + 1 )

What mistake you did?

=> You left the answer at x - 5 which is wrong. It has further solution to considered valid.

Hope it helps