Question

in an AP the 9th term is-72 and the 10th term is 60 less than 4th term find the 1 term

Answer 1

Answer: 8

Step-by-step explanation:

9th term ⇒ a + 8d = -72       ..................(1)

Also , 10th term = 4rth term - 60

⇒a +9d = (a+ 3d) - 60

⇒a + 9d - a - 3d = -60

⇒6d= -60

⇒d = -10

Substituting d= -10 in (1)

⇒a + 8 x -10 = -72

⇒a -80 = -72

⇒a = 80 -72 = 8

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Answer 2

Answer:

• Therefore, first term of AP = 8.

Explanation:

• 9th term of AP, a₉ = -72
• 10th term of AP, a₁₀ = a₄ - 60

To Find:

• First term of AP, a₁.

Now, it is given that.

⇒a₉ = - 72

⇒ a + 8d = -72       ........(1)

It is also given that,

⇒ a₁₀ = a₄ - 60

⇒ a + 9d = a + 3d - 60

⇒ 6d = - 60

⇒ d = -60/6

⇒ d = -10

Hence, Common difference = -10.

Now, put the value of d in equation (1),

⇒ a + 8d = -72

⇒ a + 8(-10) = -72

⇒ a - 80 = -72

⇒ a = -72 + 80

⇒ a = 8

Therefore, first term of AP = 8.