Question

Tìm x biết \(7^{x+2}+2.7^{x-1}=345\)

Answer 1

7^x+2+2.7^x-1=345

=>7^x-1(7³+2)=345

=>7^x-1=345:345=1

=>x-1=0

=>x=1

Answer 2

7^x-1 . 7^x+3 + 2. 7^x-1 = 345

7^x-1 .(7^x+3 + 2)  =345

7^x-1. (7^x+3 + 2) = 7^x+3 -2

7^x-1                    =(7^x+3 - 2) : (7^x+3 +2)

7^x-1                    = 0

=> x-1                  = 1

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