Question

find the surface area of a cuboid made of metal sheets whose length is15cm breadth is 12cm and height is 8cm

Answer 1

Answer:

Step-by-step explanation:

Step-by-step explanation:

Given :  

nth term , an= An + B………….(1)

On putting n = 1 in eq 1,

a1 = A + B

On putting n = 20 in eq 1,

a20 = A × 20 + B

a20 = 20A + B

a20 = l(last term)  = 20A + B

By using the formula ,Sum of nth terms , Sn = n/2 [a + l]

S20 = 20/2 [a + l]

S20 = 10 [A + B + 20A + B]

S20 = 10 [21A + 2B]

S20 = 210A + 20B

Hence, the sum of first 20 terms of the given  sequence is 210A + 20B

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