А) 28 - 11 + x= 0
D= (-11)^2 - 4 × 1 × 28 = 121 - 112 = 9 = 3^2
x1 = 11 + 3/2 × 1 = 14/2 = 7
x2 = 11 - 3/ 2 × 1 = 8/2 = 4
28 - 11 + x = ( x - 7 ) × ( x - 4)
42 - 20 x + 2x^2 = 0
D = ( -20 )^2 - 4 × 2 × 42 = 400 - 336 = 64 = 8^2
x1 = 20 + 8/ 2×2 = 28/4 = 7
x2 = 20 - 8/ 2×2 = 12/2 = 6
42 - 20x + 2x^2 = ( x - 7) × ( x - 3)
( x - 7 ) × ( x - 4 ) / ( x - 7 ) × ( x - 3 ) = x -4 / x -3
б) 6x^2 - 49x + 8 = 0
D = ( - 49 )^2 - 4 × 6 × 8 = 2401 - 192 = 2209 = 49^2
x1 = 49 + 47/ 2×6 = 96/12 = 8
x2 = 49 - 47/ 2×6 = 2/12 = 1/6
6x^2 - 49x + 8 = ( x - 8 ) × ( x - 6 )
6x^2 - 36 x - 96 = 0
D = ( - 36)^2 - 4 × 6 × ( - 96 ) = 1296 + 2304 = 3600 = 60^2
x1 = 36+60/2×6 = 96/12 = 8
x2 = 36 - 60/2×6 = - 24/12 = - 2
6x^2 - 36x - 96 = ( x - 8 ) × ( x +2 )
( x - 8 ) × ( x - 6 )/ ( x -8 ) × ( x + 2 ) = x - 6/ x + 2
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