Question

Розв'яжіть рівняння:

1) x³+5x²-4x-20=0

2) -4a(a+5)+(2a+5)²=25
СРОЧНО

Answer 1

$\displaystyle\bf\\1)\\x^{3} +5x^{2} -4x-20=0\\\\(x^{3} +5x^{2} )-(4x+20)=0\\\\x^{2} (x+5)-4(x+5)=0\\\\(x+5)(x^{2} -4)=0\\\\(x+5)(x-2)(x+2)=0\\\\\\\left[\begin{array}{ccc}x+5=0\\x-2=0\\x+2=0\end{array}\right\\\\\\\left[\begin{array}{ccc}x_{1} =-5\\x_{2} =2\\x_{3}=-2 \end{array}\right$

$\displaystyle\bf\\2)\\-4a(a+5)+(2a+5)^{2} =25\\\\-4a^{2} -20a+4a^{2} +20a+25=25\\\\25=25\\\\Otvet:a\in R$