Question

Tìm x biết:

1) 15.x-9.x+2.x=72

2) 3^x+2+3^x=10

Thanks

Answer 1

1)15x-9x+2x=(15-9+2)x=8x=72

x=72:8=9

2)3^x+2+3^x=3^x.3²+3^x=3^x.9+3^x.1=3^x.(9+1)=3^x.10=10

3^x=10:10=1

3^x=1=3⁰

=>x=0

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Answer 2

1)15x-9x+2x=72

x(15-9)+2x=72

x6+2x=72

x(6+2)=72

x8=72

x=72:8

x=9

Vay x=9

Answer 3

\(a.15x-9x+2x=72\)

\(\Rightarrow x\left(15-9+2\right)=72\)

\(\Rightarrow x.8=72\)

\(\Rightarrow x=72:8\)

\(\Rightarrow x=9\)

\(b.3^{x+2}+3^x=10\)

\(\Rightarrow3^x.3^2+3^x=10\)

\(\Rightarrow3^x\left(3^2+1\right)=10\)

\(\Rightarrow3^x.10=10\)

\(\Rightarrow3^x=1\)

\(\Rightarrow x=0\)