√ ( x + 5 ) + √ ( 2x + 8 ) = 7
( √ ( x + 5 ) + √ ( 2x + 8 ))^2 = 7^2
x + 5 + 2x + 8 + 2√ ( x + 5 )( 2x + 8 ) = 49
2√ ( 2x^2 + 8x + 10x + 40 ) = 49 - 3x - 13
√ ( 2x^2 + 18x + 40 ) = ( 36 - 13x ) : 2
√ (2x^2 + 18x + 40 ) = 18 - 7,5x
( √ ( 2x^2 + 18x + 40 ))^2 = ( 18 - 7,5x )^2
2x^2 + 18x + 40 = 324 - 270x + 56,25x^2
54,25x^2 - 288x + 284 = 0
D = 82944 - 61628 = 21316 = 146^2
x1 = ( 288 + 146 ) : 108,5 = 4
x2 = ( 288 - 146 ) : 108,5 = 142 : 108,5 = 1420/1085 = 1 335/1085 = 1 67/217
x + 5 ≥ 0 ; х ≥ - 5
2х + 8 ≥ 0 ; 2x ≥ - 8 ; x ≥ - 4