(x-1)²=2x²-6x-31
x²-2x+1=2x²-6x-31
x²-2x+1-2x²-6x-31=0
-x²+4x+32=0
x²-4x-32=0
D=16+4*32=16+128=144=12²
x1=4+12/2=8
x2=4-12/2=-4
8 / ( X + 4 ) + 16 / ( X - 4 ) = 4/3
24*( X - 4) + 48*( X + 4) = 4*(X^2 - 16)
24X - 96 + 48X + 192 = 4X^2 - 64
4X^2 - 72X - 160 = 0
4 * ( X^2 - 18X - 40) = 0
D = 324 + 160 = 484 ; √ D = 22
X1 = ( 18 + 22) : 2 = 20
X2 = ( - 4) : 2 = ( - 2 )
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X^2 - 16 ≠ 0
X^2 ≠ 16
X ≠ 4
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Ответ 20 км/час
Первый 40 - 10в=в-14
-13в=-26
в=2