Given sequence:
-2,-7,-12 ,..
Unknown;
Find the sum of the first 20 terms = ?
Solution:
The sequence is -2,-7,-12 ,..
To find he sum of n-terms of a sequence, we use the expression below;
Sₙ = 
where n is the number of terms = 20
a is the first term = -2
d is the common difference= -7 - (-)2 = -5
Now input the parameters and solve;
Sₙ = 
Sₙ = 10(-4 + -5(19)) = 10(-99) = -990
The sum of the first 20 terms of the sequence is -990
3n+2n+4=9n+12
5n+4=9n+12
4-12=9n-5n
-8=4n
Divide both sides by 4
n=-2
Answer:
6
Step-by-step explanation:
#1: 4x - 8 = 16 (You want to remove -8)
#2: 4x = 24 (In order to remove -8 you need to cancel it out, add 8 to -8, also add 8 to 16)
#3: 4x = 24 (Now you need to get the x by itself, divide 4x by 4 to only get x and also divide 24 by 4)
#4: x = 6
Rule of Thumb: If you do something to one side, to it to the other :)
Answer:
Angle DEB: 52
Angle ADB: 30
Angle CBE: 52
Angle BEC: 38
Step-by-step explanation:
Angle DEB = 52 because triangles' angles must add up to 180. Angle ADB is 30 because it is complementary to angle BDE. Angle CBE is 52 because angle BEC is complementary to BED which is 52 degrees to BEC is 38 degrees. since the angles add up to 180, and C is 90, CBE is 52. Finally, BEC is 38 because it is complementary to BED.
