Arithmetic and Geometric Progressions — Mathematics STD 10 — Question
ICSE BoardEnglish MediumSTD 10MathematicsArithmetic and Geometric Progressions2 Marks
Question
Determine the A.P. whose third term is 16 and the 7th term exceeds the 5th term by 12
✓
Answer
$ \begin{aligned} & T _3=16 \\ & T _7- T _5=12 \end{aligned} $ Let $a$ be the first term and $d$ be the common difference $ \begin{aligned} & T_3=a+2 d=16 ......(1)\\ & T_7-T_5=(a+6 d)-(a+4 d)=12 \\ & \Rightarrow a+6 d-a-4 d=12 \\ & \Rightarrow 2 d=12 \\ & \Rightarrow d=\frac{12}{2}=6 \end{aligned} $ Substitute the value of $d$ in eq. (i), we get $ \begin{aligned} & \therefore a+2 \times 6=16 \\ & \Rightarrow a+12=16 \\ & \Rightarrow a=16-12=4 \\ & \therefore \text { A.P. is } 4,10,16,22,28, \ldots \end{aligned} $
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