Question

Find the following sums 1+2+3+45+...........+20

Answer 1

Answer:

sum=n/2(a+l)

=20/2(1+20)=10(21)=210

hope it helps you

Answer 2

Answer:

210

Step-by-step explanation:

xn=f+(n-1)d

xn=1+(1n-1)

20=1n

20÷1=20

Sn=n/2(X1+Xn)

20÷2×(1+20)

10×21=210