Jika 3^x + 9^x = 90 maka nilai dari 3^x-2 adalah...

[tex] 3^{x} + 9^{x} = 90 \\
3^{x} + (3^{x})^2 = 90 [/tex]
[tex] Misal \ 3^{x} \ = \ a [/tex]
a + a² = 90
a² + a - 90 = 0
(a + 10)(a - 9) = 0

[tex] a = -10 \\
3^{x} = -10 , tidak \ memenuhi [/tex]

[tex] a = 9 \\
3^{x} = 9 [/tex]

[tex] Maka : \\
3{x-2} = \frac{3^{x}}{3^2} \\
= \frac{9}{9} \\
= 1 [/tex]