Question

已知10的a次方=20 10的b次方=5的负1次方,求9的a次方÷3的2b次方的值

Answer 1

∵10^a=20, 10^b=5^(-1)

∴a=lg20, b=-lg5

∴9^a/3^(2b)

=3^[2(a-b)]

=3^[2(lg20+lg5)]

=3^(2lg100)

=3^(2×2)

=3^4

=81