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Given two terms of the arithmetic sequence a3=25 and a8=-10 find a1 and d

Sagot :

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Answer:

Sorry I don’t know

Step-by-step explanation:

Ahishaabdelateyidn

a3=25

a8=-10

first, a3=25 will be 25= a + (3-1)×d that is the formula of the Arithimetic function genrally→ an=a (which is the first term..that we wanted in this case) + n-1 (n is the order of wanted term..we already has the term which is 3) × d (the common ration).

So, 25=a+(3-1)×d

25=a+2d

25-2d=a   rearrange

a= 25-2d

We will take this equation and subsitute it in the other equation which is -10=a+ (8-1)×d

so it will be -10=25-2d+(8-1)×d

-10= 25-2d+7d   sum the d

-10= 25+5d

-10-25= 5d

-35=5d

-35/5=d

-7= d

Now that we have the d we can go back to the equation of a= 25-2d and know the value of a

a= 25-2×-7

a1=39

d=-7

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