X ( км/час ) собственная скорость
8 = ( 45 / ( Х + 3 ) ) + ( 45 / ( Х - 3 ))
Х > 0 ; Х не равен 3
8 * ( Х^2 - 9 ) = 45 * ( Х - 3 ) + 45 * ( Х + 3 )
8Х^2 - 72 = 45Х - 135 + 45Х + 135
8Х^2 - 90X - 72 = 0
D = 8100 + 2304 = 10404 ; V D = 102
X1 = ( 90 + 102 ) : 16 = 12
X2 = ( 90 - 102 ) : 16 = - 0,625 ( < 0 )
Ответ 12 км/час
Вот 1 и 2 номер,остальное решу ,скину
<span>1. 25 - 36p</span>²<span>c</span>² = 5²-(6рс)² = (5-6рс)(5+6рс)
<span>(3+y)</span>²<span> - 4 = (3+у)</span>²-2² = (3+у-2)(3+у+2) = (у+1)(у+5)<span>
(3x+1)</span>²<span> - (4x-3)</span>² = (3х+1-4х+3)(3х+1+4х-3) = (-х+4)(7х-2)<span>
100 - 49x</span>²<span>y</span>² = 10²-(7ху)² = (10-7ху)(10+7ху)<span>
(5+x)</span>²<span> - 9 = (5+х)</span>²-3² = (5+х-3)(5+х+3) = (х+2)(х+8)<span>
(2a + 7)</span>²<span> - (3a - 5)</span>² = (2а+7-3а+5)(2а+7+3а-5) = (-а+12)(5а+2)
<span>
2. x</span>²ⁿ<span> - 9 = (х</span>ⁿ)²-3² = (хⁿ-3)(хⁿ+3)<span>
b</span>²<span> - a</span>⁴ⁿ = b² - (a²ⁿ)² = (b-a²ⁿ)(b+a²ⁿ)<span>
x</span>²ⁿ<span> - y</span>²ⁿ = (хⁿ)²-(уⁿ)² = (хⁿ-уⁿ)(хⁿ+уⁿ)<span>
81a</span>⁸ⁿ<span> - 16 = (9а</span>⁴ⁿ)²-4² = (9а⁴ⁿ-4)(9а⁴ⁿ+4) = (3а²ⁿ-2)(3а²ⁿ+2)(9а⁴ⁿ+4)<span>
a</span>²ⁿ<span> - 1 = (а</span>ⁿ)²-1² = (аⁿ-1)(аⁿ+1)<span>
x</span>²<span>- y</span>⁴ⁿ = х²-(у²ⁿ)² = (х-у²ⁿ)(х+у²ⁿ)<span>
a</span>⁴ⁿ<span> - b</span>⁴ⁿ = (а²ⁿ)²-(b²ⁿ)² = (a²ⁿ-b²ⁿ)(a²ⁿ+b²ⁿ) = (aⁿ-bⁿ)(aⁿ-bⁿ)(a²ⁿ+b²ⁿ)<span>
49x^6m</span><span> - 25 = (7x^3m)</span>² - 5² = (7x^3m - 5)(7x^3m + 5)
