Answer:
15
Step-by-step explanation:
a represents 15
13/a= 39/45
We multiply 13*3 to get the denominator 39 on the right hand side.
So this means if we multiply the numerator by 3, we also multiply the denominator by 3 as well.
So, if 13*3= 39, then what number will give us 45?
To get that number, we divide 3 into 45 to get 15
Therefore a is 15
Step-by-step explanation:
an object and its shadow create a right-angled triangle.
2 objects and their shadows create 2 similar right-angled triangles.
that means the angles are the same, and the side lengths of one triangle all correlate with the corresponding side lengths of the other triangle via the same factor.
so,
42 × f = 6
f = 6/42 = 1/7
the length of Joel's shadow is then
20 × f = 20 × 1/7 = 2.857142857... ft
We are given the first term and the common ratio, this means they belong to a geometric series.
For the given series:

Each term of the geometric series is obtained by multiplying the previous term by common ratio.
So the next terms will be:
-4.5, -6.75, -10.125, -15.1875, -22.78125
The general formula for the G.P would be:

On plotting the series, the result will be like this:
If x=3+bi, then

You know that
then

Two possible complex numbers satisfy these conditions:

As you can see the possible value of b is 2.
Answer: correct choice is A.