Question

helo friends help me plz....

Answer 1

Answer:

Sn=n/2{2a+(n-1)d}

Step-by-step explanation:

a=3

d=5-3=2

n=20

S20=20/2{2×3+(20-1)2}

=10{6+19×2}

=10{6+38}

=10{44}

=440

mark it brainliest answer

give thanks

have a nice day

Answer 2

$\huge\boxed{\underline{\underline{\red{Solution}}}}$

$\longmapsto$ARITHMETIC PROGRESSION

An Arithmetic Progression is a progression of numbers such that the difference between the a term & it's successor is constant(Same)

This Difference is called Common Difference

Generally First Term is denoted by a &

Common Difference is denoted by d

$\longmapsto$FORMULA FOR SUM

The sum of the first n terms is

$\displaystyle = \frac{n}{2} \ \{ 2a + (n - 1)d \: \}$

$\longmapsto$CALCULATION

The given AP is

$3 , 5 , 7 ,...................$

First Term = a = 3

Common Difference = d = 5-3 = 2

Hence the

$sum \: of \: the \: {20} \: \: terms$

$\displaystyle = \frac{20}{2} \ \{ 2 \times 3 + (20 - 1) \times 2\}$

$\displaystyle = 10 \times (6 + 38 )$

$\displaystyle = 10 \times 44$

$\displaystyle = 440$