1.rút gọn: a,(2x+7)²-4)(x-5)(x+5) b,(x-2)mũ3-(x+3x+9)+6.(x-2)²
2.a,(3x-5)²-9(x-2)(x+2)=7
b,4x²-28x+49=25
c,(x+1)mũ 3 – (x-2)(x²+2x+4)-3(x²-2)=5
1.rút gọn: a,(2x+7)²-4)(x-5)(x+5) b,(x-2)mũ3-(x+3x+9)+6.(x-2)² 2.a,(3x-5)²-9(x-2)(x+2)=7 b,4x²-28x+49=25 c,(x+1)mũ 3 – (x-2)(x²+2x+4)
By Gianna
Đáp án:
a) (2x+3)²-3(x-4)(x+4)=(x-2)²+1
=> 4x²+12x+9-(3x-12)(x+4)=(x²-4x+4)+1
=> 4x²+12x+9-3x²-12x+12x+28-x²+4x-4-1=0
=> 16x+32=0
=>x= -2
Vậy x=-2
b) (3x-2)(9x²+6x+4)-(3x-1)(9x²-3x+1)=x-4
=> 27x³+18x²+12x-18x²-12x-8-(27x³-9x²+3x-9x²+3x-1)-x+4=0
=> 27x³+18x²+12x-18x²-12x-8-27x³+9x²-3x+9x²-3x+1-x+4=0
=> 18x²-7x+7=0(vô lí)
Vậy phương trình trên vô nghiệm
c) x(x-1)-(x-3)(x+4)=5x
=> x²-x-(x²+4x-3x-12)-5x=0
=> x²-x-x²-4x+3x+12-5x=0
=> -7x+12=0
=> x=12/7
Vậy x=12/7
d) (2x+1)(2x-1)=4x(x-7)-3x
=> 4x²-2x+2x-1-4x²+28x+3x=0
=> 31x-1=0
=> x=1/31
Vậy x=1/31
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