2lg((x-y)除以2)=lgx+lgy,
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(x+2y)(x—y)=2xy整理得x²-xy-2y²=0因为xy均>0所以等号两边同时除以xy设x/y=t整理得t-1-2/t=0剩下的你自己接就行了~
∵lg(x-y)+lg(x+2y)=lg2+lgx+lgy,∴lg(x-y)(x+2y)=lg2xy.∴(x-y)(x+2y)=2xy,即(x-2y)(x+y)=0.再由x、y都是正数可得x+y≠0,
(x-y)(x+3y)=2^2*xyx^2+2xy-3y^2=4xyx^2-2xy-3y^2=0(x+y)(x-3y)=0x=-y,x=3y由定义域x>0,y>0x=-y不成立x=3yx/y=3
lg(x+2y)+lg(x-y)=lg2+lgx+lgylg(x+2y)(x-y)=lg2xy(x+2y)(x-y)=2xyx^2+xy-2y^2=2xyx^2-xy-2y^2=0(x-2y)(x+y
选择B因为又跟号和lg要保证sinx>0cosx>0所以2kπ再问:不对吧sinx>=0吧?再答:有等号我忘了,不好意思那就是A
若使函数y=lg(2−x)的解析式有意义则lg(2-x)≥0=lg1即2-x≥1解得x≤1故函数y=lg(2−x)的定义域是(-∞,1]故答案为:(-∞,1]
2lg(x-2y)=lgy+lgx即(x-2y)^2=xy(x-y)(x-4y)=0又x>2y>0故x=4y所以log2(x/y)=2
有题可知:x+2y>0;x-4y>0;x>0;y>0可得:x/y>4原式化简为:lg(x+2y)(x-4y)=lg2xy所以:(x+2y)(x-4y)=2xy化简:x^2-4xy-8y^2=0同除y^
. -y)+lg(x+2y)=lg[(x-y)(x+2y)]lg^2+lgx+lgy=lg(2xy)所以:(x-y)(x+2y)=2xyx^2+2xy-xy-2y^2=2xyx^2-2y^2
(x-y)(x+2y)=2xyx^2+2xy-xy-2y^2=2xyx^2-2y^2=xyx/y-2y/x=1设a=x/y则有a^2-a-2=0(a-2)(a+1)=0a=2,-1.根据题意取正所以:
lg(x-y)+lg(x-2y)=lg2+lgx+lgylg(x-y)(x-2y)=lg2xyx^2-2xy-xy+2y^2=2xyx^2-5xy+2y^2=0(x/y)^2-5(x/y)+2=0x/
由题知,lg[(x-y)/(x-2y)]=lg(2xy)得(x-y)/2xy=x-2y,x+1/2x-2y-1/2y=0x/y=1.
lg(x+y)+lg(2x+3y)=lg12+lgx+lgylg[(x+y)(2x+3y)]=lg(12xy)(x+y)(2x+3y)=12xy2x^2+5xy+3y^2=12xy=02x^2-7xy
(x-3)(x-2)
lg(xyz)=lg(x)+lg(y)+lg(z)lg(x²y²z的-3次方)=2lg(x)+2lg(y)-3lg(z)
答:lg(x-3y)^2=lg4xy(x-3y)^2=4xyx^2-6xy+9y^2=4xyx^2-10xy+9y^2=0(x-y)(x-9y)=0x=yorx=9yy/x=1ory/x=1/9
2lg(x-3y)=lgx+lg(4y)lg(x-3y)²=lg(4xy)(x-3y)²=4xyx²-6xy+9y²-4xy=0x²-10xy+9y&
lg(2-x)-lg(x-1)>0lg(2-x)>lg(x-1)∴2-x>x-1>0∴1
由lg(x-y)+lg(7x-8y)=2,得lg(x-y)(7x-8y)=2(x-y)(7x-8y)=100(1)由2^(-x+3y)=4,得-x+3y=2x=3y-2(2)把(2)代入(1)得2(y
2lg((x-y)/2)=lg(((x-y)/2)^2)=lgx+lgy=lg(xy)lg(((x-y)/2)^2)=lg(xy)((x-y)/2)^2=xy((x-y)^2)/4=xyx2-2xy+