K is the force constant of a spring. The work done is increasing its extension from l_(1) to l_(2) will be

K is the force constant of a spring. The work done is increasing its e

1.	K is the force constant of a spring. The work done is increasing its extension from l_(1) to l_(2) will be
Answer» `K (l_2 - l_1)` `K//2(l_2+l_1)` `K(l_2^2 - l_1^2)` `K/2 (l_2^2 - l_1^2)` ANSWER :D