Tính biểu thức sau đây

To find the sum of the given series, we can group the terms into two separate sums: the sum of the first five terms (21+23+25+27+29) and the sum of the last five terms (-31-33-35-37-39).

The sum of the first five terms can be calculated using the formula for the sum of an arithmetic series:

Sum = (n/2)(first term + last term)
= (5/2)(21 + 29)
= (5/2)(50)
= 125

The sum of the last five terms can also be calculated using the formula for the sum of an arithmetic series:

Sum = (n/2)(first term + last term)
= (5/2)(-31 + -39)
= (5/2)(-70)
= -175

Finally, we can find the total sum by subtracting the sum of the last five terms from the sum of the first five terms:

Total Sum = 125 - 175
= -50

Therefore, the sum of the given series is -50.