(a + b)2 = a2 + 2ab + b2<span> (a – b)2 = a2 – 2ab + b2</span><span>a2 – b2 = (a – b)(a + b)</span><span>(a + b – c)2 = a2 + b2 + c2 + 2ab – 2ac – 2bc</span><span>(a + b + c)2 = a2 + b2 + c2 + 2ab + 2ac + 2bc</span>
Х - скорость течения реки
11+х - скорость теплохода по течению
11-х - скор теплохода против течения
t=S/V
![\frac{60}{11+x}+\frac{60}{11-x}+5=16](https://tex.z-dn.net/?f=%5Cfrac%7B60%7D%7B11%2Bx%7D%2B%5Cfrac%7B60%7D%7B11-x%7D%2B5%3D16)
![60(x-11)-60(x+11)=11(x^2-121)\\\\11x^2=1331-1320\\\\11x^2=11\\\\x^2=1\\\\x=\pm 1\\\\Otvet:\; x=1\; km/chas](https://tex.z-dn.net/?f=60%28x-11%29-60%28x%2B11%29%3D11%28x%5E2-121%29%5C%5C%5C%5C11x%5E2%3D1331-1320%5C%5C%5C%5C11x%5E2%3D11%5C%5C%5C%5Cx%5E2%3D1%5C%5C%5C%5Cx%3D%5Cpm%201%5C%5C%5C%5COtvet%3A%5C%3B%20x%3D1%5C%3B%20km%2Fchas)
(x+4)(x-4)-(x-3)^2 = x^2-16-(x^2-6x+9)=x^2-16-x^2+6x-9=6x-25
Под буквой а) ответ 400
под буквой б) ответ 5/8