can anyone show me how this is factorised? 2x^2-11x-21 thx?

Go here to learn how to factor trinomials in general:
http://www.purplemath.com/modules/factquad.htm

(see especially page 2)

- multiply outer integers: 2 * (-21) = -42
- find factors of -42 which add up to -11: 3 and -14
- so far, we have: 2x^2 + 3x - 14x - 21
- "grouping": x(2x + 3) - 7(2x + 3), which is equal to (x - 7)(2x + 3)

You should check out the site that Geezah recommended.

2x^2 - 11x - 21
= 2x^2 + 3x - 14x - 21
= (2x^2 + 3x) - (14x + 21)
= x(2x + 3) - 7(2x + 3)
= (2x + 3)9x - 7)

(2x + 3)(x - 7)

2X^2 - 11x - 21 =

2X^2 -14x + 3 x - 21 x =

(2x+3)(x-7)

(2x +3)(x-7)

2x^2-11x-21

= 2x2 - 14x + 3x - 21

= 2x( x - 7 ) + 3(x - 7)

= (x - 7)* ( 2x +3)

When u have (px + a )* (qx + b) = pqx^2 + (qa + pb)x + ab

x(2x-11-21/x)


or

x^2( 2-11/x-21/x^2)

or

x^3(2/x-11/x^2-21/x^3)

or

...