There are 13 left-handed and 21 right-handed spirals on the cacti in the photograph. what is special about these numbers?
a. the value of the 21st term of the fibonacci sequence is 13.
b. they are consecutive terms in the pyramidal sequence.
c. they are consecutive terms in the fibonacci sequence.
d. the value of the 21st term of the pyramidal sequence is 13.

C.They are consecutive terms in the Fibonacci sequence.

Step-by-step explanation:

The Fibonacci Sequence is the series of numbers: 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, ...

Each number is the sum of the two numbers that come before it.

The square pyramidal numbers are: 1, 5, 14, 30, 55, 91, 140, 204, 285, 385, 506, 650, 819, ...

Therefore, we can see given numbers of cactus , 13 and 21 respectively are the consecutive terms of Fibonacci sequence.

Thus, Option C is the right answer.

step-by-step explanation:

the largest number of the four options is 1.8 x 10-2

you have it in scientific notation.

1.80 x 10-6   = 0.00000180

1.80 x 10-4   = 0.000180 (bigger, or "less small", than the former one)

so

1.8 x 10-2       = 0.0180. as you see. the "less small", or the biggest one of them all.

as you have negative exponent, it means you are dividing 1.8 by 100 (i.e. moving the dot towards left, two times).

if you had positive exponent for the scientific notation, power of tenths, you would be multiplying times 100 (moving the dot towards right) as below:

1.8 x (10)2 = 180

so. if you have negative exponent in scientific notation, move the dot toward left. if it is positive, toward right as many times the exponent tells you.