Maths Special 01

Maths Special 01

(For Class 10th)

Q. If 4th term of an A.P. is zero then prove that the 25th term of the A.P. is 3 times its 11th terms.

Sol.

a₄ = 0

a­₂₅ = 3(a₁₁)

LHS = RHS

Taking LHS

a₂₅          = a + 24d

                   = (a + 3d) + 21d

                   = 0 + 21d

                   = 21d

RHS

3(a₁₁) = 3 [(a + 10d)]

                   = 3[(a + 3d) + 7d]

                   = 3[(0 + 7d]

= 3[7d]

= 21d

LHS = RHS so that it is proved that a₂₅ = 3(a₁₁)