Help me with my equations plz !!! (1 Viewer)

[v sia]

Factorise
6y^2 + 47y-8

this question takes me a while to do , becausei have to do a lot of guess work. Is there a much faster way of doing this

i start of by doing this

( ) ( )

(3y ) (2y )
(6y ) ( y )

shit like that help plz

 

[Heinz]

Originally posted by v sia
Factorise
6y^2 + 47y-8

this question takes me a while to do , becausei have to do a lot of guess work. Is there a much faster way of doing this

i start of by doing this

( ) ( )

(3y ) (2y )
(6y ) ( y )

shit like that help plz

i personally do the cross-swords method

you write 6y^2 as a product of its factors

6y -8
y +1

then you cross multiply to get the y term out. 6y*1 +8*y. this doesnt add up to -47. so you switch it to make

6y +1
y -8

This works out so your factors are the horizontal lines.

 

[Heinz]

You can do the cross swords methods which i personally use or use the quadratic equation to find the roots, in this case the roots are 1/6 and -8. so if theyre the roots then (y-1/6) and (y+8) are factors. so the equation becomes (6y-1)(y+8)

 

[kimmeh]

use quadratic equation in terms of y and the you have "roots" or values that solve that equation to get zero. ie:

[- b +/- sq. root (b^2 - 4ac) ] / 2a
= [ - 47 +/- sq. rt (47^2 - 4 x 6 x -8)] / ( 2 x 6)
= [ - 47 +/- 49 ] / 12
.: y = 1/6 or -8
.: factorise: ( y + 8 ) ( 6y -1 )

this is how i work out this kind of stuff when i cant be bothered tp use my brain

 

[Collin]

Just do lots of practice quadratic trinomial questions, and your reaction and thinking time for these kinds of problems decrease dramatically over time.

Or if you're lazy like kimmeh and myself at certain times, just apply the quadratic equation to your hearts' content.