4^x + 4^-x=7 maka 8^x +8^-x =

jawab

4ˣ + 4⁻ˣ = (2ˣ)² + (2⁻ˣ)² = 7
(2ˣ + 2⁻ˣ)² - 2.(2ˣ . 2⁻ˣ)  = 7
(2ˣ + 2⁻ˣ)² - 2(1) = 7
(2ˣ+ 2⁻ˣ)² = 9
(2ˣ + 2⁻ˣ) = 3

(8ˣ + 8⁻ˣ) = (2ˣ)³ + (2⁻ˣ)³
= (2ˣ + 2⁻ˣ)³ - 3(2ˣ. 2⁻ˣ)(2ˣ+2⁻ˣ)
= (3)³ - 3(1)(3)
= 27- 9
= 18