The right approach would be:
4n - (2n - 6)
4n - 2n + 6
2n+6
The options confused me. So pick the answer based on the solution.
Since there are only 4 terms in the sum, it's not too much work to expand it as

Alternatively, we can use the well-known formulas


These sums start at n = 0, so in our given sum we will keep track of the 0-th term separately:

as expected.
Answer: 120 degrees
Explanation: Flat surfaces are equal to 180 degrees. 180 minus 60 is 120.
-9 < 6 -v < 9 . . . . two inequalities
-15 < -v < 3 . . . . . subtract 6
-3 < v < 15 . . . . . . multiply by -1
Answer:
1/2
Step-by-step explanation:
Since the recessive gene is carried in the x chromosome and a father can only pass it to a daughter, the father doesn't have the disease nor carries it.
The mother carries the recessive gene because her father passed her his conditioned gene (only having one x chromosome), while her mother gave her a normal one so she can have normal vision.
The chance of having a boy or a girl is 1/2 and the chance of this baby of having both recessive gene is null because in order to have a girl that is color blind both her x chromosomes must have the recessive gene, but the father can't pass it since he doesn't carries it. Therefore the combined probability is 1/2*(1-0) = 1/2.