Question

Simplify the expression (4x − 3)(x + 5). 4x2 − 17x + 15 4x2 − 17x − 15 4x2 + 17x + 15 4x2 + 17x − 15

Answer 1

a)
`(4x-3)(x+5)=`


`*(a+b)(c+d)=ac+ad+bc+bd`


`Soo..`


`4x*x+4x*5-3*x-3*5=`


`=4 x^(2) +20x-3x-15`


`=4x^(2) +17x-15`

b)
`4x^(2) -17x+15=`


`=(4x-5)(x-3)`

c)
`4 x^(2) -17x-15=`


`=(4x+3)(x-5)`

d)
`4 x^(2) +17x+15=`

`=(4x+5)(x+3)`


e)
`4 x^(2) +17x-15=`

`=(4x-3)(x+5)`

Answer 2

There are mnemonic acronyms out there for reminding you how to do this. I think of it simply as using the distributive property.
(4x-3)(x+5) = 4x(x+5) -3(x+5)
then again
= (4x² +20x) + (-3x -15)
= 4x² + (20-3)x -15 . . . . . . . combine like terms
= 4x² +17x -15