Question

3+8+13+....+x= 2265.x is_?

Answer 1

Given : 3+8+13+....+x= 2265

To Find :  Value of x

Solution:

3+8+13+....+x= 2265

3+8+13+....+x

this is an AP

a = 3  d  = 5

x = 3 + (n - 1)5

=> x  = 3 + 5n - 5

=> 5n = x + 2

=> n = (x + 2)/5

Sum = (n/2)(3 + x)  

= ((x + 2)/10)(3 + x)  = 2265

=> x² + 5x + 6  = 22650

=> x² + 5x  -  22644 = 0

=> x² +153x - 148x -  22644 = 0

=> (x + 153)(x - 148) = 0

=> x = - 153 , x = 148

Hence x = 148

Value of x = 148

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