First term ,a=4 , common difference =4-7=-3, n =50
sum of first 50terms= (50/2)[2×4+(50-1)(-3)]
=25×[8+49]×-3
=25×57×-3
=25× -171
= -42925
derivation of the formula for the sum of n terms
Progression, S
S=a1+a2+a3+a4+...+an
S=a1+(a1+d)+(a1+2d)+(a1+3d)+...+[a1+(n−1)d] → Equation (1)
S=an+an−1+an−2+an−3+...+a1
S=an+(an−d)+(an−2d)+(an−3d)+...+[an−(n−1)d] → Equation (2)
Add Equations (1) and (2)
2S=(a1+an)+(a1+an)+(a1+an)+(a1+an)+...+(a1+an)
2S=n(a1+an)
S=n/2(a1+an)
Substitute an = a1 + (n - 1)d to the above equation, we have
S=n/2{a1+[a1+(n−1)d]}
S=n/2[2a1+(n−1)d]
Answer:
distribute 2 inside the parenthesis
Step-by-step explanation:
Answer:
400
Step-by-step explanation:
382.993 is lies between 300 and 400
and 400 is nearest hundred of 382.993
If you add up all of the digits in the number, and if that number you get is able to be divided by 3, the original number is good to divide by 3.
For example: 618
You add 6+1+8 and get 15
Take 15 and divide by 3
You get a whole number, 5
Therefore, 618 can be divided by 3
Answer:
A
Step-by-step explanation:
