Toán Lớp 6: (x-5) . (2x-4) = 5
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Toán Lớp 6: (x-5) . (2x-4) = 5
giải giúp mk vs ạ mk đang cần gấp
Comments ( 2 )
=> \(\left[ \begin{array}{l}x – 5 = 0\\2x – 4 = 0\end{array} \right.\)
=> \(\left[ \begin{array}{l}x = 0 + 5\\2x = 4\end{array} \right.\)
=> \(\left[ \begin{array}{1}x = 5\\x=2\end{array} \right.\)
Vậy x ∈ {5 ; 2}
(x-5) . (2x-4) = 5
=>x.(2x-4)-5.(2x-4)=5
=>2x^2-4x-10x+20=5
=>2x^2-4x-10x+20-5=0
=>2x^2+(-4x-10x)+15=0
=>2x^2-14x+15=0
=>2.(x^2-7.x+15/2)=0
=>x^2-7x+15/2=0
=>x^2-2.x. 7/2+(7/2)^2-19/4=0
=>x^2-x . 7/2-x. 7/2+7/2 . 7/2=0+19/4
=>x.(x-7/2)-7/2 . (x-7/2)=19/4
=>(x-7/2)(x-7/2)=19/4
=>(x-7/2)^2=19/4
=>(x-7/2)^2=(+-sqrt{19}/2)^2
=>[(x-7/2=sqrt{19}/2),(x-7/2=-sqrt{19}/2):}
=>[(x=(sqrt{19}+7)/2),(x=(-sqrt{19}+7)/2):}
=>[(x=(7+sqrt{19})/2),(x=(7-sqrt{19})/2):}
Vậy x=(7+sqrt{19})/2 hoặc x=(7-sqrt{19})/2
Nếu đề là:(x-5)(2x-4)=0
=>[(x-5=0),(2x-4=0):}
=>[(x=0+5),(2x=0+4):}
=>[(x=5),(2x=4):}
=>[(x=5),(x=4:2):}
=>[(x=5),(x=2):}
Vậy x=5 hoặc x=2