Question

4) 2y4 - 5y2 – 7 = 0
СРОЧНО ДАЮ 15 БАЛОВ​

Answer 1

Ответ:

$2y ^ { 4 } -5y ^ { 2 } -7=0 \\y ^ { 2 }=t\\2t ^ { 2 } -5t -7=0 \\D=25-4*2*-7=81\\\sqrt{D} =9\\x_{1} =\dfrac{5+9}{4} =\dfrac{14}{4} =\dfrac{7}{2}\\x_{2} =\dfrac{5-9}{4} =\dfrac{-4}{4} =-1\\t=y ^ { 2 }\\y=\sqrt{t} =\sqrt{\dfrac{7}{2}}= \dfrac{\sqrt{7} }{\sqrt{2} }=\dfrac{\sqrt{7}*\sqrt{2} }{\sqrt{2} *\sqrt{2} }=\dfrac{\sqrt{14} }{2 }\\y=-\sqrt{t} =-\sqrt{\dfrac{7}{2}}= -\dfrac{\sqrt{7} }{\sqrt{2} }=-\dfrac{\sqrt{7}*\sqrt{2} }{\sqrt{2} *\sqrt{2} }=-\dfrac{\sqrt{14} }{2 }$

Объяснение: