Question

-x^2+3x+40 factoring quadratic expressions help please? i'v tried everything I know I cant figure it out I factored and the only multiples that get 3 is 5 and 8 but when I put them into the equation to check it I cant get it to come out right for nothing

Answer 1

-x^2+3x+40 =-(x^2-3x-40)=-(x^2-2.x.3/2+9/4-9/4-40)=-{(x-3/2)^2-(13/2)^2}=(13/2)^2-(x-3/2)^2=(13/2+x-3/2)(13/2-x+3/2)=(5+x)(8-x)

Answer 2

@_YouDontKnowHer_

Answer 3

whoa that is a lot of stuff way different from how I got taught lol but thank you I will do my best to see what you did and figure it out

Answer 4

Will I do in short??

Answer 5

@_YouDontKnowHer_

Answer 6

\[-x^2+3x+40=-x^2+8x-5x+40=-x(x-8)-5(x-8)=(-x-5)(x-8)=(x+5)(8-x)\]

Answer 7

if you want to it's just the way we learned it this is how I do it
-x^2+3x+40
factors of 40 are 1*40, 2*20, 4*10, and 5*8
which of the factors equal the middle number 3
8-5 is 3 so 8 and 5 are the only factors that will fit
so always put the bigger number in the parenthesis first ex. -(x+8)-(x+5) drop down your first sign + then multiply positive times the other sign positive equals positive so your other sign is also positive that's how I got both my signs then this is where I got stuck checking it
-(x+8)-(x+5)
-x*-x= -x^2
-x*+5= -5
8*-x= -8x
8*5=40
so then that gives you the equation -x^2-5-8x+40 but -5-8x isnt a positive 3 so I dont know what I did wrong

Answer 8

@jango_IN_DTOWN

Answer 9

YOu saw my solution? Which line do you have a problem?

Answer 10

you made a mistake here

Answer 11

it will be -x(x-8)-5(x-8)

Answer 12

@_YouDontKnowHer_