V ( x + 6 ) + V ( x + 1 ) = V ( 7x + 4 )
( V ( 7x + 4 ))^2 = ( V ( x + 6 ) + V ( x + 1 ))^2
7x + 4 = x + 6 + x + 1 + 2V ( x + 6 )( x + 1 )
7x + 4 - 2x - 7 = 2V( x + 6 )( x + 1 )
( 5x - 3 )^2 = ( 2V ( x + 6 )( x + 1 ))^2
25х^2 - 30х + 9 = 4( Х + 6 )( Х + 1 )
25х^2 - 30х + 9 = 4( х^2 + Х + 6х + 6 )
25х^2 - 30х + 9 = 4х^2 + 28х + 24
21х^2 - 58х - 15 = 0
D = 3364 + 1260 = 4624 = 68^2
X1 = ( 58 + 68 ) : 42 = 3
X2 = ( 58 - 68 ) : 42 = - 10/42 = - 5/21
ОДЗ
1) Х + 6 >= 0 ; Х >= - 6
2) Х + 1 >= 0 ; Х >= - 1
3) 7х + 4 >= 0 ; Х >= - 4/7