Let an equal the number of ternary strings of length n made up of os, .ls, and 2s, such that the substrings 00, 01, 10, and 11 never occur. prove that an = an-l +2an-2, (n 2: 2), with ao = 1 and al =3. then find a formula for an.

Look at the figure below: triangle abc is a right triangle with angle abc equal to 90 degrees. the length of ac is 5 units and the length of ab is 4 units. d is a point above c. triangle adc is a right triangle with angle dac equal to 90 degrees and dc parallel to ab. what is the length, in units, of segment cd?