## College Algebra (6th Edition)

Sum even integers between 21 and 45 = 22 + 24 + 26+ 28+........+44 First term $a_{1}$ = 22 Last term $a_{l}$= 44 Common difference (d)= 2 Number of terms = $\frac{(Last term - first term)}{difference (d)}$ + 1 Number of terms (n) = $\frac{(44 - 22)}{2}$ + 1 = $\frac{22}{2}$ + 1 = 11 + 1 = 12 Sum of n terms = $\frac{n}{2}$($a_{1}$ + $a_{n}$) = $\frac{n}{2}$($a_{1}$ + $a_{l}$) = $\frac{12}{2}$(22 + 44) = 6$\times$66 Sum 12 even integers between 21 and 45 = 22 + 24 + 26+ 28+........+44= 396