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Determinați mulțimea soluțiilor fiecărei ecuații:​

Determinați Mulțimea Soluțiilor Fiecărei Ecuații class=

Răspuns :

Răspuns:

[tex]a)x^2=9= > x=\sqrt{9} = > x=3,-3\\\\b)3x^2=12= > x^2=12:3= > x=\sqrt{4} = > x=2,-2\\\\c)2x^2-72=0= > 2x^2=72= > x^2=72:2= > x=\sqrt{36} = > x=6,-6\\\\d)(x-2)^2=25= > x-2=\sqrt{25} = > x=5+2= > x=7\\\\x=-2+5= > x=-3\\\\e)(2x-3)^2=25= > 2x-3=\sqrt{25} = > 2x=5+3= > x=8:2= > x=4\\\\2x=-5+3= > x=-1\\\\f) (2x+1)^2=49= > 2x+1=\sqrt{49} = > 2x=7-1= > x=6:2= > x=3\\\\2x+1=-7= > x=-4\\\\g)(2x+5)^2=81 = > 2x+5=\sqrt{81} = > 2x+5=9= > 2x=9-5= > x=2\\\\2x+5=-9= > x=-7\\\\h)2x-5=11= > 2x=11+5= > x=16:2= > x=8\\\\2x-5=-11= > x=-3[/tex]

Avem pătrate perfecte la fiecare, deci ne putem folosi de identitatea:
[tex] \boxed{\sqrt{x^2} =|x| } \, \ \ \forall x\in \mathbb{R} [/tex]
La fel și cu cele cu paranteză.
Punctul a)
[tex] x^2 =9 \implies \sqrt{x^2}=\sqrt{9} \\ |x|=3 \implies \tt x \in\{ -3,3\} [/tex]

Punctul b)
[tex] 3x^2 =12 \implies x^2 =4 \\ \sqrt{x^2} =\sqrt{4} \implies |x| =2 \\ \tt x \in \{-2,2\} [/tex]

Punctul c)
[tex] 2x^2 -72=0 \implies 2x^2 =72 \\ x^2 =36 \implies \sqrt{x^2} =\sqrt{36} \\ |x| =6 \implies \tt x\in \{-6,6\} [/tex]

Punctul d)
[tex] (x-2)^2 =25 \implies \sqrt{(x-2)^2}=\sqrt{25} \\ |x-2| =5 \implies x-2 =5 \ \ sau \ \ x-2=-5 \\ \tt x \in \{-3,7\} [/tex]

Punctul e)
[tex] (2x-3)^2 =25 \implies \sqrt{(2x-3)^2}=\sqrt{25} \\ |2x-3| =5 \implies 2x-3=5 \ \ sau \ \ 2x-3 =-5 \\ 2x=8 \ \ sau \ \ 2x=-2 \\ \tt x\in \{-1, 4 \} [/tex]

Punctul f)
[tex] (2x+1)^2 =25 \implies \sqrt{(2x+1)^2}=\sqrt{25} \\ |2x+1| =5 \implies 2x+1=5 \ \ sau \ \ 2x+1 =-5 \\ 2x=4 \ \ sau \ \ 2x=-6 \\ \tt x\in \{-3, 2 \} [/tex]

Punctul g)
[tex] (2x+5)^2 =25 \implies \sqrt{(2x+5)^2}=\sqrt{25} \\ |2x+5| =5 \implies 2x+5=5 \ \ sau \ \ 2x+5 =-5 \\ 2x=0 \ \ sau \ \ 2x=-10 \\ \tt x\in \{-5, 0 \} [/tex]

Punctul h)
[tex] (2x-5)^2 =25 \implies \sqrt{(2x-5)^2}=\sqrt{25} \\ |2x-5| =5 \implies 2x-5=5 \ \ sau \ \ 2x-5 =-5 \\ 2x=10 \ \ sau \ \ 2x=0 \\ \tt x\in \{0, 5 \} [/tex]