Площадь квадрата равна площади прямоугольника, одна из сторон которого на 5 м больше а другая на 4 м меньше стороны квадрата. найти длину стороны квадарата

пусть х см - сторона квадрата, тогда (х+5) м - одна сторона прямоугольника, (х-4) м - другая сторона прямоугольника, т.к. площади квадрата и прямоугольника равны, получаем:

(х+5) (х-4) = х² 

х² - 4х + 5х - 20 - х² = 0 

х - 20 = 0

х = 20

20 м - длина стороны квадрата.

ответ. 20 м. 

sкв=sпр.

а кв=х м

а пр=х+5 м

b пр=x-4 м

x^2=(x+5)(x-4)

x^2=x^2-4x+5x-20

х=20

сторона квадрата 20м.

(x⁴-x²-12)/(x³+1)> 0 метод интервалов: 1. (x⁴-x²-12)/(x³+1)=0 x⁴-x²-12=0 или x³+1≠0 x⁴-x²-12=0 биквадратное уравнение, x²=t, t> 0 t²-t-12=0. t₁=4, t₂=-3. -3< 0. t=-3 посторонний корень, => t=4 обратная замена: t=4. x²=4. x₁=-2, x₂=2 x³+1≠0, x³≠-1. x≠-1 (x-2)*(x+2)*(x²+3)/(x³+1)> 0           -           +             -               + 2. > x x∈(-2; -1)∪(2; ∞)

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