Question

(v) Find the roots using, the quadratic formula :-
(a) x² + 4x + 5 = 0 b) 3x square - 5x + 2 = 0
vi) In and AP if the sth and 12th term are 30 and 65 respectively, what is the sum of first 20 terms ?

pleas help me
that I will mark you as brainist​

Answer 1

Step-by-step explanation:

5th term = 30

a + 4d = 30..........(1)

12th term = 65

a + 11d = 65.........(2)

Sub (1) from (2)

7d = 35

d = 5

so, a + 4×5 = 30

a + 20 = 30

a = 10

Sum of 20 terms =

$\frac{20}{2} (2 \times 10 + (20 - 1) \times 5) \\ = 10(20 + 95) \\ = 10 \times 115 \\ = 1150$