Toán Lớp 8: Tìm x: 6x^2-15x-(2x-5)(2x+5)=0
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Toán Lớp 8: Tìm x: 6x^2-15x-(2x-5)(2x+5)=0
Comments ( 2 )
<=>6x^2-15x-[(2x)^2-5^2]=0
<=>6x^2-15x-(4x^2-25)=0
<=>6x^2-15x-4x^2+25=0
<=>(6x^2-4x^2)-15x+25=0
<=>2x^2-15x+25=0
<=>2x^2-10x-5x+25=0
<=>2x.(x-5)-5.(x-5)=0
<=>(2x-5)(x-5)=0
<=>[(2x-5=0),(x-5=0):}
<=>[(2x=5),(x=5):}
<=>[(x=5/2),(x=5):}
Vậy x\in{5/2;5}