(1)已知a:b:c=2:3:5.求(10a+12b+5c)÷(a+b+c)值
5个回答
1.
令a=2k,b=3k,c=5k
(10a+12b+5c)÷(a+b+c)
=(20k+36k+25k)÷(2k+3k+5k)
=81÷10
=8.1
2.
x=1-a^(-b)
a^(-b)=1-x
a^b=1/(1-x)
y=1+a^b=1+1/(1-x)=(2-x)/(1-x)
3.
3^n=1/27=3^(-3)
n=-3
2^n+1=1/8+1=9/8
4.
x^2-4x+1=0
x-4+1/x=0
x+1/x=4
(x+1/x)^2=16
x^2+2+1/x^2=16
x^2+x^(-2)=14
5.
3a-[(a^2+4a+4)÷(a+2)]+[(a^2+6a+9)÷(a+3)]
=3a-[(a+2)^2÷(a+2)]+[(a+3)^2÷(a+3)]
=3a-(a+2)+(a+3)
=3a+1
6.
A/B=99^9/9^99÷11^9/9^90
=(99^9/11^9)*(9^90/9^99)
=9^9*9^(-9)
=9^0
=1
A=B
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