Toán Lớp 8: tìm x biết :
a) 2x^2+16x+32=0
b) (3x-5)^2-25x^2=0
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Toán Lớp 8: tìm x biết :
a) 2x^2+16x+32=0
b) (3x-5)^2-25x^2=0
Comments ( 2 )
2x^2+16x+32=0
<=>2.(x^2+8x+16)=0
<=>x^2+8x+16=0:2
<=>x^2+2.x.4+4^2=0
<=>(x+4)^2=0
<=>x+4=0
<=>x=-4
Vậy x=-4
b)
(3x-5)^2-25x^2=0
<=>(3x-5)^2-(5x)^2=0
<=>(3x-5-5x)(3x-5+5x)=0
<=>(-2x-5)(8x-5)=0
<=>[(-2x-5=0),(8x-5=0):}
<=>[(-2x=5),(8x=5):}
<=>[(x=-5/2),(x=5/8):}
Vậy x\in{-5/2;5/8}