Answer:
-84
Explanation:
The formula for the nth term of a geometric progression is
Un = ar^n- 1
The sum of the first six terms of a geometric series (U6) = 21/16
Common ratio = -1/2 ,
a = First term ??
21/16 = a × (-1/2 )^6- 1
21/16 = a ×(-2^-1)^5
21/16 = a × -2^-6
Cross Multiply
16 × a × -2^-6 = 21
a = 21/16 × -2^-6
a = 21/16 ×- 1/2⁶
a = 21/16 × -1/64
a = 21 ÷(-1/4)
a = 21 × -4
a = -84
The first term = 84