factoring trinomials

[glad crescent]

Factor the expression

3y^2 - 25y + 28

How do i do this

[lament karma]

(3y-4)(y-7)

[glad crescent]

I got (3y+3)(y-28x)

how did u get that

[lament karma]

so what i did was

first look at 3y^2

you can rewrite that as 3y times y

and look at 28

you need to pick factors of 28

such that when you multiply one of the factors by 3 and add the other you get -25

so one of them were 7 and 4

3(-7)=-21 and -4(y)=-4y

and -21-4=-25

so it would be (3y-4)(y-7)

[glad crescent]

Ok i understand

but one thing

[lament karma]

yeah?

[glad crescent]

Could you explain this

[lament karma]

sure

lets just look at (3y-4)(y-7)

when you expand this you get 3y(y-7)-4(y-7)

this will be equal to 3y^2-21y-4y+28

so basically the factors of 28 in this case was 7 and 4

basically i multiplied 3y by -7 to get -21y

and you add that number by the other factor which was -4y

-21y-4y=-25y

[glad crescent]

Oh

[lament karma]

yea

[glad crescent]

I get it know

Thank you very much

[lament karma]

np

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