help with some factorising (1 Viewer)

[Loz_metalhead]

I just cant get the right answers...I have this book with lots of questions...please help


x^2/x^2+3x+2 - 2x/x+2


p^6-26p^3-27

c+d/c^-1 + d^1


(3m-n)^3 - (2m-3n)^3


I feel so stupid.

 

[Loz_metalhead]

also 3x^2+2x-4=o (solve by completing the square)

my yearlies are coming up..I suck

 

[香港!]

I just cant get the right answers...I have this book with lots of questions...please help


x^2/x^2+3x+2 - 2x/x+2


p^6-26p^3-27

c+d/c^-1 + d^1


(3m-n)^3 - (2m-3n)^3


I feel so stupid.

HiHi... can you put brackets into places where necessary please, cuz things like...
"x^2/x^2+3x+2 - 2x/x+2"
it would mean 1+3x+2-......
but i guess u mean factorise x²\(x²+3x+2)-2x\(x+2)??
x²\(x²+3x+2)-2x\(x+2)=x²\(x+2)(x+1)-2x\(x+2)
=[x²-2x(x+1)]\(x+1)(x+2)
=(-x²-2x)\(x+1)(x+2)
=-x(x+2)\(x+1)(x+2)
=-x\(x+1)
you can go further if you want but that looks neat enough i guess...

"p^6-26p^3-27"
=(p³+1)(p³-27)
=(p³+1³)(p³-3³)
=(p+1)(p²-p+1)(p-3)(p²+3p+9)
Here I used a³+b³=(a+b)(a²-ab+b²)
and also a³-b³=(a-b)(a²+ab+b²)

"c+d/c^-1 + d^1"
wat do u mean??
y do u put a c^-1 on there?

"(3m-n)^3 - (2m-3n)^3"
just use a³-b³=(a-b)(a²+ab+b²) treating "3m-n" as 'a' and "2m-3n" as 'b'

 

[香港!]

also 3x^2+2x-4=o (solve by completing the square)

my yearlies are coming up..I suck

3x²+2x-4=0
x²+2x\3=4\3
x²+2x\3+(2\6)²=4\3+(2\6)²
(x+2\6)²=13\9
x+2\6=+- (sqrt 13)\3
.: x=-2\6+(sqrt 13)\3=(-1+sqrt13)\3
or x=-2\6-(sqrt 13)\3=(-1-sqrt13)\3

 

[Loz_metalhead]

you got the first wrong but I worked it anyway...these are just questions from a book. Thanks for the help

 

[香港!]

..................

 

[Loz_metalhead]

how does -2/6 become -1?

 

[香港!]

how does -2/6 become -1?

-2/6 does not become -1... not in what I wrote atleast

 

[Loz_metalhead]

x=-2\6+(sqrt 13)\3=(-1+sqrt13)\3


WoudlI be incorrect it I put x=-2\6+(sqrt 13)\3...the -1 answer is in the back of the book.

 

[香港!]

x=-2\6+(sqrt 13)\3=(-1+sqrt13)\3


WoudlI be incorrect it I put x=-2\6+(sqrt 13)\3...the -1 answer is in the back of the book.

you won't be "incorrect", however... depending on how the marking criteria is... you MIGHT lose a mark in the exam for not doing an easy simplification...

 

[香港!]

-2\6+(sqrt 13)\3
=-2\6 + 2(sqrt 13)\(3x2)
=-2\6+(2sqrt13)\6
=(-2+2sqrt 13)\6
divide out the 2
=(-1+sqrt 13)\3