Question

3ˣ ₊ 3ˣ ⁻ ¹ ₊ 3ˣ ⁻² ₊ 3ˣ ⁻ ³ = 40

Answer 1

$3^x+3^{x-1}+3^{x-2}+3^{x-3}=40|\cdot 3^3 \\27\cdot 3^x+9\cdot 3^{x}+3\cdot 3^x+3^x=1080\\3^x(27+9+3+1)=1080\\3^x\cdot 40=1080\\3^x=27\\3^x=3^3\\\boxed{x=3}$

Answer 2

3^(x-3) (3³+3²+3+1)=40

3^(x-3) (27+9+3+1)=40

3^(x-3) *40=40

3^(x-3)=1=3^0

x-3=0

x=3