In the first series, the summation applies to the whole (2n+3) inside
the parentheses, so the 3 gets summed up 5 times.
But in the second one, the summation only applies to the 2n , so
the 3 is only added after the summation is finished.
The difference between five 3s the first time and one 3 the second time
is your 12 .
9514 1404 393
Answer:
140°
Step-by-step explanation:
Angles 1 and 3 are "corresponding" angles, so are congruent.
∠1 = ∠3
20x +60 = 30x +20
40 = 10x . . . . . . . . . . . . subtract 20x+20
4 = x . . . . . . . . . . . . . . divide by 10
∠1 = 20x +60 = 20(4) +60 = 80 +60
∠1 = 140°
