8. If a=10 and d=3 for an A.P. find the*sum of the first 15 terms.Your

1.	8. If a=10 and d=3 for an A.P. find the*sum of the first 15 terms.Your answer
Answer» Answer: $\huge \boxed{s_{15} = 465}$ Step-by-step EXPLANATION: → Given:- a=10 (FIRST term) d=3 (COMMON difference) → To Find:- $s_{15} \: (sum \: of \: 15 \: terms)$ → Formula Used:- $s_{n} = \frac{n}{2} \times [2a + (n - 1) \times d]$ → SOLUTION:- $s_{n} = \frac{n}{2} \times [2a + (n - 1) \times d] \: ,where \: \boxed{a = 10}, \: \boxed{d = 3} \: and \: \boxed{ n = 15}$ $\implies s_{15} = \frac{15}{2} [2(10) + (15 - 1)(3)]$ $\implies s_{15} = \frac{15}{2} [2(10) + (14)(3)]$ $\implies s_{15} = \frac{15}{2} \times 2 [10 + (7)(3)]$ $\implies s_{15} = 15 (10 + 21)$ $\implies s_{15} = 15 \times 31$ $\implies \boxed{s_{15} = 465}$ THEREFORE, Therefore,The Sum of 15 terms of this A.P. is 465. → One More formula to Remember:- $a_n = a + ( n- 1) \times d$