1. Twenty first and twenty second terms of an AP are 64 and 70
a) Find the common difference
b) Find the first term.
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Answer: first term = -56, common difference = 6
Step-by-step explanation:
The common difference of an AP is the difference between two consecutive terms
d(common difference) = 70 - 64 = 6
Using the formula; l = a + (n-1)*d where
l= Given term of the series
a= first term of the series
n= number of terms between the first term and the given term
d= common difference
Let us take the 21st term and substitute in the formula
64 = a + (21-1)*6
=> a = 64 - 120 = -56
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