Factorise y4 - 3y^2 - 4. Hint. Let z = y^2

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- Apr 11th 2010, 10:38 PMAJShawFactorise
Factorise y4 - 3y^2 - 4. Hint. Let z = y^2

- Apr 11th 2010, 10:40 PMharish21
- Apr 11th 2010, 10:44 PMAJShaw
I am just learning factorising. Is it:

z^2-3z-4

z^2-3z-4

z-3-4

z-7

If not right, can you show me how to do it please? - Apr 11th 2010, 10:48 PMharish21
What you have done is not right. Please review your class notes/book about factorizing!

$\displaystyle z^2-3z-4$

$\displaystyle = z^2-(4-1)z - 4$

$\displaystyle = z^2 - 4z + z - 4$

$\displaystyle = z(z-4) + 1(z-4)$

$\displaystyle =(z+1)(z-4)$

Now substitute the value of z that you had assumed at the beginning of the quesiton.