Answer:
B. -21a-15
Step-by-step Explanation:
Answer: First Option : Sₙ= n/2(a₁ + aₙ)
Step-by-step explanation:
The nth partial sum of an arithmetic sequence or the sum of the first n terms of the arithmetic series can be defined as the sum of a finite number of term in an arithmetic sequence.
It is calculated using the formula:
Sₙ= n/2(a₁ + aₙ)
Where :
a₁ = First term
aₙ = last term
n = number of terms
Answer:
30degrees
Step-by-step explanation:
Given
Exterior angle m<CDE = 7x - 19 degrees
interior angles are
m<BCD = 2x - 1
m<DBC = x+10
Since the sum of the interior angles is equal to the exterior, hence;
2x - 1 + x+10 = 7x - 19
3x + 9 = 7x - 19
3x - 7x = -19 - 9
-4x = -28
x = 28/4
x = 7
Get m<CDE
m<CDE = 7x - 19
m<CDE = 7(7) - 19
m<CDE = 49 - 19
m<CDE = 30degrees
Answer:
a = 9
Step-by-step explanation:
2(a + 7) = 5a - 13
We want to bring a to one side, I will choose to bring it to the right
First, expand the bracket by multiplying 2 with a + 7
2a + 14 = 5a - 13
Bring the -13 to the left by adding 13 to both sides
2a + 14 + 13 = 5a - 13 + 13
Simplify
2a + 27 = 5a
Bring the 2a to the right by subtracting 2a from both sides
2a - 2a + 27 = 5a - 2a
Simplify
27 = 5a - 2a
27 = 3a
Bring the 3 to the left by dividing both sides by 3
27÷3 = a
Simplify
a = 9
