Answer:
B.
Step-by-step explanation:
Because google said so
∆PQR and ∆SQT are similar, so corresponding sides occur in fixed ratios with one another. This means
SQ / PQ = ST / PR
Solve for x :
8 / ((x + 5) + 8) = (x - 9) / 21
8 / (x + 13) = (x - 9) / 21
168 = (x - 9) (x + 13)
168 = x² + 4x - 117
x² + 4x - 285 = 0
(x + 19) (x - 15) = 0
⇒ x = -19 or x = 15
But x can't be smaller than 9, otherwise ST = x - 9 would be a negative length. So x = 15.
The part (10 + c) represents a sum because a sum is the result of an addition expression/equation, you only need to find the part of the expression that uses addition.
The correct option is D): "an=1/n" because:
<span>since first term: n is 1,
if you plug in 1 in the 1/n,
you get one.
second term: n=2,
so, 1/n = 1/2.</span>