In exercise 9.5, question 5:
 
Show that:
 
1. (3x+7)^2 - 84x = (3x-7)^2

Please explain the solution.
Thanks!

Asked by abusami309 | 26th Dec, 2016, 11:54: PM

Expert Answer:

begin mathsize 16px style L. H. S. equals left parenthesis 3 x plus 7 right parenthesis squared minus 84 x
equals left parenthesis 3 x right parenthesis squared plus 2 cross times 3 x cross times 7 plus left parenthesis 7 right parenthesis squared minus 84 x
equals 9 x squared plus 42 x plus 49 minus 84 x
equals 9 x squared plus 42 x minus 84 x plus 49
equals 9 x squared minus 42 x plus 49
equals left parenthesis 3 x right parenthesis squared minus 2 cross times 3 x cross times 7 plus left parenthesis 7 right parenthesis squared
equals left parenthesis 3 x minus 7 right parenthesis squared
equals R. H. S.

I d e n t i t i e s space u s e d colon
left parenthesis a plus b right parenthesis squared equals a squared plus 2 a b plus b squared
left parenthesis a minus b right parenthesis squared equals a squared minus 2 a b plus b squared end style

Answered by Rashmi Khot | 27th Dec, 2016, 08:52: AM