1) a^2 - 10a +25 = ( a - 5 )^2

2) 25 - a^2 = ( 5 + a )( a - 5 )

3) ( b - 1 )( a - 5 ) = - ( 1 - b )( a - 5 )

4) ( a - 1 )( 2a - 5 ) = 2a^2 + 2a - 5

1)a^2 - 10a +25 = ( a - 5 )^2              ( a - 5 )^2=a^2-10a+25

   a^2-10a+25=a^2-10a+25

  a^2-10a+25-a^2+10a-25=0

  0=0

2)25 - a^2 = ( 5 + a )( a - 5 )            3)( b - 1 )( a - 5 ) = - ( 1 - b )( a - 5 ) 

   25-a^2-5a+a^2+25a-5a=0                ( b - 1 )( a - 5 )=(b+1)(a - 5)

  15a+25=0                                             ba-a-5b-ba-a+5b+5=0

   15a=-25                                               2a+5=0

    a=-25/-15                                            2a=-5

    a=5/3                                                    a=-5/-2

                                                                  a=2.5