Question

(3x+4)(3x-5) how to do it by using identities

Answer 1

Hi friend!
Its my pleasure to help you with this question :-)

_________________________________
Given to solve (3x+4)(3x-5)

Here let us use the identity :

(p+a)(p+b)=x^2+(a+b)p+ab

where p=3x
a=4
b=-5

Now lets solve
___________

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

=(3x)^2+(4-5)3x+4*-5

=9x^2+-3x-20
___________
___________

HOPE IT HELPS DEAR FRIEND
________________________

Answer 2

Hi

★nice question★

★ thanks★

given,

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

now

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

= ( 3x )² - 5 × 3x + 4 × 3x - 5 × 4

= 9x² - 15x + 12x - 20

= 9x² - 3x - 20

= 9x² - ( 15 - 12 ) x - 20

= 9x² - 15x + 12x - 20

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

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

either

3x - 5 = 0 or 3x + 4 = 0

=> x = 5/3 => x = -4/3

===================================