Question

How many terms of ap 20 16 12 be added so that sum be 56?

Answer 1

a=20
d=-4
refer to the attachment
hope it helps you dear

Answer 2

Answer:

5 and 12

Step-by-step explanation:

AP-> 16,14,12

sum=n/2{2a+(n-1)d}

60=n/2{2*16+(n-1)(-2)}

120=n{34-2n}

120=34n-2n2

n2 -17n+60=0

n2 -12n-5n+60=0

n(n-12)-5(n-12)=0

n=5,12

here,the common difference is negative therefore terms go on diminishing and 9th term becomes zero.All terms after 9th term are negative.These negative terms when added to the positive terms from 6th to 8th term , they cancel out each other and the sum remains the same.

hope it helps ..