Question

for an ap t4 is 12 and d is - 10 find a​

Answer 1

Answer:

a4 = a + 3d

12 = a + 3× (-10)

12 = a - 30

12 +30 = a

42 = a

Answer 2

Answer:

a =42

*PL go through the explanation very sincerely and ur topic will be cleared to a great extent

Explanation:

Let's first note what is given

t4=12 , d =-10 , n=4

to find - a

now here are some formulae u need to remember to solve AP sums

1) tn=a+ (n-1) *d

2) sn = n/2 [2a+(n-1) *d]

ok , so now heading for the sum

we are given value of t4

so we can apply formula no 1 and substitute the given values (in simple language I am just putting values in the formula )

tn=a+(n-1)*d

t4=a + ( 4-1)*-10

= a + (3)*-10

12 =a + (-30)

now shifting -30 to lhs

(cause we want value of a )

Therefore,

12+30=a

Thus , a =42

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